Mailing List Archive: [syzbot] [xfs?] possible deadlock in xfs_ilock_data_map

[syzbot] [xfs?] possible deadlock in xfs_ilock_data_map_shared

syzbot+b7e8d799f0ab724876f9 at syzkaller

Apr 25, 2024, 7:46 AM

Post #1 of 4 (2 views)

Hello,

syzbot found the following issue on:

HEAD commit: 977b1ef51866 Merge tag 'block-6.9-20240420' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126497cd180000
kernel config: https://syzkaller.appspot.com/x/.config?x=d239903bd07761e5
dashboard link: https://syzkaller.appspot.com/bug?extid=b7e8d799f0ab724876f9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/08d7b6e107aa/disk-977b1ef5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9c5e543ffdcf/vmlinux-977b1ef5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/04a6d79d2f69/bzImage-977b1ef5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b7e8d799f0ab724876f9@syzkaller.appspotmail.com

XFS (loop2): Ending clean mount
======================================================
WARNING: possible circular locking dependency detected
6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0 Not tainted
------------------------------------------------------
syz-executor.2/7915 is trying to acquire lock:
ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:312 [inline]
ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:3746 [inline]
ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:3827 [inline]
ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: kmalloc_trace+0x47/0x360 mm/slub.c:3992

but task is already holding lock:
ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&xfs_dir_ilock_class){++++}-{3:3}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
down_write_nested+0x3d/0x50 kernel/locking/rwsem.c:1695
xfs_reclaim_inode fs/xfs/xfs_icache.c:945 [inline]
xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1631 [inline]
xfs_icwalk_ag+0x120e/0x1ad0 fs/xfs/xfs_icache.c:1713
xfs_icwalk fs/xfs/xfs_icache.c:1762 [inline]
xfs_reclaim_inodes_nr+0x257/0x360 fs/xfs/xfs_icache.c:1011
super_cache_scan+0x411/0x4b0 fs/super.c:227
do_shrink_slab+0x707/0x1160 mm/shrinker.c:435
shrink_slab+0x1092/0x14d0 mm/shrinker.c:662
shrink_one+0x453/0x880 mm/vmscan.c:4774
shrink_many mm/vmscan.c:4835 [inline]
lru_gen_shrink_node mm/vmscan.c:4935 [inline]
shrink_node+0x3b17/0x4310 mm/vmscan.c:5894
kswapd_shrink_node mm/vmscan.c:6704 [inline]
balance_pgdat mm/vmscan.c:6895 [inline]
kswapd+0x1882/0x38a0 mm/vmscan.c:7164
kthread+0x2f2/0x390 kernel/kthread.c:388
ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 (fs_reclaim){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
__fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
might_alloc include/linux/sched/mm.h:312 [inline]
slab_pre_alloc_hook mm/slub.c:3746 [inline]
slab_alloc_node mm/slub.c:3827 [inline]
kmalloc_trace+0x47/0x360 mm/slub.c:3992
kmalloc include/linux/slab.h:628 [inline]
add_stack_record_to_list mm/page_owner.c:177 [inline]
inc_stack_record_count mm/page_owner.c:219 [inline]
__set_page_owner+0x561/0x810 mm/page_owner.c:334
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
prep_new_page mm/page_alloc.c:1541 [inline]
get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
__alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
__alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399
xfs_lookup+0x298/0x550 fs/xfs/xfs_inode.c:640
xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:303
lookup_open fs/namei.c:3475 [inline]
open_last_lookups fs/namei.c:3566 [inline]
path_openat+0x1035/0x3240 fs/namei.c:3796
do_filp_open+0x235/0x490 fs/namei.c:3826
do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
do_sys_open fs/open.c:1421 [inline]
__do_sys_openat fs/open.c:1437 [inline]
__se_sys_openat fs/open.c:1432 [inline]
__x64_sys_openat+0x247/0x2a0 fs/open.c:1432
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(&xfs_dir_ilock_class);
lock(fs_reclaim);
lock(&xfs_dir_ilock_class);
lock(fs_reclaim);

*** DEADLOCK ***

3 locks held by syz-executor.2/7915:
#0: ffff8881d0472420 (sb_writers#14){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:409
#1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: inode_lock include/linux/fs.h:795 [inline]
#1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: open_last_lookups fs/namei.c:3563 [inline]
#1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: path_openat+0x7d3/0x3240 fs/namei.c:3796
#2: ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114

stack backtrace:
CPU: 1 PID: 7915 Comm: syz-executor.2 Not tainted 6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
__fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
might_alloc include/linux/sched/mm.h:312 [inline]
slab_pre_alloc_hook mm/slub.c:3746 [inline]
slab_alloc_node mm/slub.c:3827 [inline]
kmalloc_trace+0x47/0x360 mm/slub.c:3992
kmalloc include/linux/slab.h:628 [inline]
add_stack_record_to_list mm/page_owner.c:177 [inline]
inc_stack_record_count mm/page_owner.c:219 [inline]
__set_page_owner+0x561/0x810 mm/page_owner.c:334
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
prep_new_page mm/page_alloc.c:1541 [inline]
get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
__alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
__alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399
xfs_lookup+0x298/0x550 fs/xfs/xfs_inode.c:640
xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:303
lookup_open fs/namei.c:3475 [inline]
open_last_lookups fs/namei.c:3566 [inline]
path_openat+0x1035/0x3240 fs/namei.c:3796
do_filp_open+0x235/0x490 fs/namei.c:3826
do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
do_sys_open fs/open.c:1421 [inline]
__do_sys_openat fs/open.c:1437 [inline]
__se_sys_openat fs/open.c:1432 [inline]
__x64_sys_openat+0x247/0x2a0 fs/open.c:1432
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f23c887dea9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f23c95950c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f23c89abf80 RCX: 00007f23c887dea9
RDX: 000000000000275a RSI: 0000000020000080 RDI: ffffffffffffff9c
RBP: 00007f23c88ca4a4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f23c89abf80 R15: 00007fff62a26428
</TASK>

---
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Re: [syzbot] [xfs?] possible deadlock in xfs_ilock_data_map_shared [ In reply to ]

djwong at kernel

Apr 26, 2024, 9:32 AM

Post #2 of 4 (2 views)

Permalink

On Thu, Apr 25, 2024 at 07:46:28AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 977b1ef51866 Merge tag 'block-6.9-20240420' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=126497cd180000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d239903bd07761e5
> dashboard link: https://syzkaller.appspot.com/bug?extid=b7e8d799f0ab724876f9
> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/08d7b6e107aa/disk-977b1ef5.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/9c5e543ffdcf/vmlinux-977b1ef5.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/04a6d79d2f69/bzImage-977b1ef5.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b7e8d799f0ab724876f9@syzkaller.appspotmail.com
>
> XFS (loop2): Ending clean mount
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0 Not tainted
> ------------------------------------------------------
> syz-executor.2/7915 is trying to acquire lock:
> ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:312 [inline]
> ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:3746 [inline]
> ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:3827 [inline]
> ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: kmalloc_trace+0x47/0x360 mm/slub.c:3992
>
> but task is already holding lock:
> ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&xfs_dir_ilock_class){++++}-{3:3}:
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> down_write_nested+0x3d/0x50 kernel/locking/rwsem.c:1695
> xfs_reclaim_inode fs/xfs/xfs_icache.c:945 [inline]
> xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1631 [inline]
> xfs_icwalk_ag+0x120e/0x1ad0 fs/xfs/xfs_icache.c:1713
> xfs_icwalk fs/xfs/xfs_icache.c:1762 [inline]
> xfs_reclaim_inodes_nr+0x257/0x360 fs/xfs/xfs_icache.c:1011
> super_cache_scan+0x411/0x4b0 fs/super.c:227
> do_shrink_slab+0x707/0x1160 mm/shrinker.c:435
> shrink_slab+0x1092/0x14d0 mm/shrinker.c:662
> shrink_one+0x453/0x880 mm/vmscan.c:4774
> shrink_many mm/vmscan.c:4835 [inline]
> lru_gen_shrink_node mm/vmscan.c:4935 [inline]
> shrink_node+0x3b17/0x4310 mm/vmscan.c:5894
> kswapd_shrink_node mm/vmscan.c:6704 [inline]
> balance_pgdat mm/vmscan.c:6895 [inline]
> kswapd+0x1882/0x38a0 mm/vmscan.c:7164
> kthread+0x2f2/0x390 kernel/kthread.c:388
> ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> -> #0 (fs_reclaim){+.+.}-{0:0}:
> check_prev_add kernel/locking/lockdep.c:3134 [inline]
> check_prevs_add kernel/locking/lockdep.c:3253 [inline]
> validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
> __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> __fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
> fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
> might_alloc include/linux/sched/mm.h:312 [inline]
> slab_pre_alloc_hook mm/slub.c:3746 [inline]
> slab_alloc_node mm/slub.c:3827 [inline]
> kmalloc_trace+0x47/0x360 mm/slub.c:3992
> kmalloc include/linux/slab.h:628 [inline]
> add_stack_record_to_list mm/page_owner.c:177 [inline]
> inc_stack_record_count mm/page_owner.c:219 [inline]
> __set_page_owner+0x561/0x810 mm/page_owner.c:334
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
> prep_new_page mm/page_alloc.c:1541 [inline]
> get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
> __alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
> __alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
> alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
> xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
> xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
> xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
> xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
> xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
> xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
> xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
> xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
> xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
> xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399

Hm. We've taken an ILOCK in xfs_dir_lookup, and now we're reading a
directory block. We don't have PF_MEMALLOC_NOFS set, nor do we pass
GFP_NOFS when allocating the xfs_buf pages.

Nothing in this code path sets PF_MEMALLOC_NOFS explicitly, nor does it
create a xfs_trans_alloc_empty, which would set that. Prior to the
removal of kmem_alloc, I think we were much more aggressive about
GFP_NOFS usage.

Seeing as a lookup could involve walking a dabtree, we probably want the
empty transaction to guard against dabtree cycle livelocks. This would
be a good time to change xfs_bmapi_read to take a transaction parameter.

--D

> xfs_lookup+0x298/0x550 fs/xfs/xfs_inode.c:640
> xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:303
> lookup_open fs/namei.c:3475 [inline]
> open_last_lookups fs/namei.c:3566 [inline]
> path_openat+0x1035/0x3240 fs/namei.c:3796
> do_filp_open+0x235/0x490 fs/namei.c:3826
> do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
> do_sys_open fs/open.c:1421 [inline]
> __do_sys_openat fs/open.c:1437 [inline]
> __se_sys_openat fs/open.c:1432 [inline]
> __x64_sys_openat+0x247/0x2a0 fs/open.c:1432
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> rlock(&xfs_dir_ilock_class);
> lock(fs_reclaim);
> lock(&xfs_dir_ilock_class);
> lock(fs_reclaim);
>
> *** DEADLOCK ***
>
> 3 locks held by syz-executor.2/7915:
> #0: ffff8881d0472420 (sb_writers#14){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:409
> #1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: inode_lock include/linux/fs.h:795 [inline]
> #1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: open_last_lookups fs/namei.c:3563 [inline]
> #1: ffff888056da8338 (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: path_openat+0x7d3/0x3240 fs/namei.c:3796
> #2: ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114
>
> stack backtrace:
> CPU: 1 PID: 7915 Comm: syz-executor.2 Not tainted 6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
> check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
> check_prev_add kernel/locking/lockdep.c:3134 [inline]
> check_prevs_add kernel/locking/lockdep.c:3253 [inline]
> validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
> __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
> lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> __fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
> fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
> might_alloc include/linux/sched/mm.h:312 [inline]
> slab_pre_alloc_hook mm/slub.c:3746 [inline]
> slab_alloc_node mm/slub.c:3827 [inline]
> kmalloc_trace+0x47/0x360 mm/slub.c:3992
> kmalloc include/linux/slab.h:628 [inline]
> add_stack_record_to_list mm/page_owner.c:177 [inline]
> inc_stack_record_count mm/page_owner.c:219 [inline]
> __set_page_owner+0x561/0x810 mm/page_owner.c:334
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
> prep_new_page mm/page_alloc.c:1541 [inline]
> get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
> __alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
> __alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
> alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
> xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
> xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
> xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
> xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
> xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
> xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
> xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
> xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
> xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
> xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399
> xfs_lookup+0x298/0x550 fs/xfs/xfs_inode.c:640
> xfs_vn_lookup+0x192/0x290 fs/xfs/xfs_iops.c:303
> lookup_open fs/namei.c:3475 [inline]
> open_last_lookups fs/namei.c:3566 [inline]
> path_openat+0x1035/0x3240 fs/namei.c:3796
> do_filp_open+0x235/0x490 fs/namei.c:3826
> do_sys_openat2+0x13e/0x1d0 fs/open.c:1406
> do_sys_open fs/open.c:1421 [inline]
> __do_sys_openat fs/open.c:1437 [inline]
> __se_sys_openat fs/open.c:1432 [inline]
> __x64_sys_openat+0x247/0x2a0 fs/open.c:1432
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f23c887dea9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f23c95950c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
> RAX: ffffffffffffffda RBX: 00007f23c89abf80 RCX: 00007f23c887dea9
> RDX: 000000000000275a RSI: 0000000020000080 RDI: ffffffffffffff9c
> RBP: 00007f23c88ca4a4 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007f23c89abf80 R15: 00007fff62a26428
> </TASK>
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup
>

Re: [syzbot] [xfs?] possible deadlock in xfs_ilock_data_map_shared [ In reply to ]

david at fromorbit

Apr 26, 2024, 2:20 PM

Post #3 of 4 (2 views)

Permalink

[cc linux-mm@kvack.org]

On Fri, Apr 26, 2024 at 09:32:28AM -0700, Darrick J. Wong wrote:
> On Thu, Apr 25, 2024 at 07:46:28AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 977b1ef51866 Merge tag 'block-6.9-20240420' of git://git.k..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=126497cd180000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=d239903bd07761e5
> > dashboard link: https://syzkaller.appspot.com/bug?extid=b7e8d799f0ab724876f9
> > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/08d7b6e107aa/disk-977b1ef5.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/9c5e543ffdcf/vmlinux-977b1ef5.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/04a6d79d2f69/bzImage-977b1ef5.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+b7e8d799f0ab724876f9@syzkaller.appspotmail.com
> >
> > XFS (loop2): Ending clean mount
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0 Not tainted
> > ------------------------------------------------------
> > syz-executor.2/7915 is trying to acquire lock:
> > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:312 [inline]
> > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:3746 [inline]
> > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:3827 [inline]
> > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: kmalloc_trace+0x47/0x360 mm/slub.c:3992
> >
> > but task is already holding lock:
> > ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114
> >
> > which lock already depends on the new lock.
> >
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #1 (&xfs_dir_ilock_class){++++}-{3:3}:
> > lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> > down_write_nested+0x3d/0x50 kernel/locking/rwsem.c:1695
> > xfs_reclaim_inode fs/xfs/xfs_icache.c:945 [inline]
> > xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1631 [inline]
> > xfs_icwalk_ag+0x120e/0x1ad0 fs/xfs/xfs_icache.c:1713
> > xfs_icwalk fs/xfs/xfs_icache.c:1762 [inline]
> > xfs_reclaim_inodes_nr+0x257/0x360 fs/xfs/xfs_icache.c:1011
> > super_cache_scan+0x411/0x4b0 fs/super.c:227
> > do_shrink_slab+0x707/0x1160 mm/shrinker.c:435
> > shrink_slab+0x1092/0x14d0 mm/shrinker.c:662
> > shrink_one+0x453/0x880 mm/vmscan.c:4774
> > shrink_many mm/vmscan.c:4835 [inline]
> > lru_gen_shrink_node mm/vmscan.c:4935 [inline]
> > shrink_node+0x3b17/0x4310 mm/vmscan.c:5894
> > kswapd_shrink_node mm/vmscan.c:6704 [inline]
> > balance_pgdat mm/vmscan.c:6895 [inline]
> > kswapd+0x1882/0x38a0 mm/vmscan.c:7164
> > kthread+0x2f2/0x390 kernel/kthread.c:388
> > ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
> > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> >
> > -> #0 (fs_reclaim){+.+.}-{0:0}:
> > check_prev_add kernel/locking/lockdep.c:3134 [inline]
> > check_prevs_add kernel/locking/lockdep.c:3253 [inline]
> > validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
> > __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
> > lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> > __fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
> > fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
> > might_alloc include/linux/sched/mm.h:312 [inline]
> > slab_pre_alloc_hook mm/slub.c:3746 [inline]
> > slab_alloc_node mm/slub.c:3827 [inline]
> > kmalloc_trace+0x47/0x360 mm/slub.c:3992
> > kmalloc include/linux/slab.h:628 [inline]
> > add_stack_record_to_list mm/page_owner.c:177 [inline]
> > inc_stack_record_count mm/page_owner.c:219 [inline]
> > __set_page_owner+0x561/0x810 mm/page_owner.c:334
> > set_page_owner include/linux/page_owner.h:32 [inline]
> > post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
> > prep_new_page mm/page_alloc.c:1541 [inline]
> > get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
> > __alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
> > __alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
> > alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
> > xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
> > xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
> > xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
> > xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
> > xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
> > xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
> > xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
> > xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
> > xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
> > xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399
>
> Hm. We've taken an ILOCK in xfs_dir_lookup, and now we're reading a
> directory block. We don't have PF_MEMALLOC_NOFS set, nor do we pass
> GFP_NOFS when allocating the xfs_buf pages.
>
> Nothing in this code path sets PF_MEMALLOC_NOFS explicitly, nor does it
> create a xfs_trans_alloc_empty, which would set that. Prior to the
> removal of kmem_alloc, I think we were much more aggressive about
> GFP_NOFS usage.

This isn't an XFS bug. The XFS code is correct - the callsite in the
buffer cache is using GFP_KERNEL | __GFP_NOLOCKDEP explicitly to
avoid these sorts of false positives.

Please take a closer look at the stack trace - there's a second
memory allocation taking place there way below the XFS memory
allocation inside the page owner tracking code itself:

static void add_stack_record_to_list(struct stack_record *stack_record,
gfp_t gfp_mask)
{
unsigned long flags;
struct stack *stack;

/* Filter gfp_mask the same way stackdepot does, for consistency */
gfp_mask &= ~GFP_ZONEMASK;
gfp_mask &= (GFP_ATOMIC | GFP_KERNEL);
gfp_mask |= __GFP_NOWARN;

set_current_in_page_owner();
stack = kmalloc(sizeof(*stack), gfp_mask);
if (!stack) {
unset_current_in_page_owner();
return;
}
unset_current_in_page_owner();
....

Look familiar? That exactly the same gfp mask filtering that the
stackdepot code was doing that caused this issue with KASAN:

https://lore.kernel.org/linux-xfs/000000000000fbf10e06164f3695@google.com/

Which was fixed with this patch:

https://lore.kernel.org/linux-xfs/20240418141133.22950-1-ryabinin.a.a@gmail.com/

Essentially, we're now playing whack-a-mole with internal kernel
debug code that doesn't honor __GFP_NOLOCKDEP....

MM-people: can you please do an audit of all the nested allocations
that occur inside the public high level allocation API and ensure
that they all obey __GFP_NOLOCKDEP so we don't have syzbot keep
tripping over them one at a time?

-Dave.
--
Dave Chinner
david@fromorbit.com

Re: [syzbot] [xfs?] possible deadlock in xfs_ilock_data_map_shared [ In reply to ]

djwong at kernel

Apr 26, 2024, 4:17 PM

Post #4 of 4 (2 views)

Permalink

On Sat, Apr 27, 2024 at 07:20:03AM +1000, Dave Chinner wrote:
> [cc linux-mm@kvack.org]
>
> On Fri, Apr 26, 2024 at 09:32:28AM -0700, Darrick J. Wong wrote:
> > On Thu, Apr 25, 2024 at 07:46:28AM -0700, syzbot wrote:
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: 977b1ef51866 Merge tag 'block-6.9-20240420' of git://git.k..
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=126497cd180000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=d239903bd07761e5
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=b7e8d799f0ab724876f9
> > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/08d7b6e107aa/disk-977b1ef5.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/9c5e543ffdcf/vmlinux-977b1ef5.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/04a6d79d2f69/bzImage-977b1ef5.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+b7e8d799f0ab724876f9@syzkaller.appspotmail.com
> > >
> > > XFS (loop2): Ending clean mount
> > > ======================================================
> > > WARNING: possible circular locking dependency detected
> > > 6.9.0-rc4-syzkaller-00266-g977b1ef51866 #0 Not tainted
> > > ------------------------------------------------------
> > > syz-executor.2/7915 is trying to acquire lock:
> > > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:312 [inline]
> > > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:3746 [inline]
> > > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:3827 [inline]
> > > ffffffff8e42a800 (fs_reclaim){+.+.}-{0:0}, at: kmalloc_trace+0x47/0x360 mm/slub.c:3992
> > >
> > > but task is already holding lock:
> > > ffff888056da8118 (&xfs_dir_ilock_class){++++}-{3:3}, at: xfs_ilock_data_map_shared+0x4f/0x70 fs/xfs/xfs_inode.c:114
> > >
> > > which lock already depends on the new lock.
> > >
> > >
> > > the existing dependency chain (in reverse order) is:
> > >
> > > -> #1 (&xfs_dir_ilock_class){++++}-{3:3}:
> > > lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> > > down_write_nested+0x3d/0x50 kernel/locking/rwsem.c:1695
> > > xfs_reclaim_inode fs/xfs/xfs_icache.c:945 [inline]
> > > xfs_icwalk_process_inode fs/xfs/xfs_icache.c:1631 [inline]
> > > xfs_icwalk_ag+0x120e/0x1ad0 fs/xfs/xfs_icache.c:1713
> > > xfs_icwalk fs/xfs/xfs_icache.c:1762 [inline]
> > > xfs_reclaim_inodes_nr+0x257/0x360 fs/xfs/xfs_icache.c:1011
> > > super_cache_scan+0x411/0x4b0 fs/super.c:227
> > > do_shrink_slab+0x707/0x1160 mm/shrinker.c:435
> > > shrink_slab+0x1092/0x14d0 mm/shrinker.c:662
> > > shrink_one+0x453/0x880 mm/vmscan.c:4774
> > > shrink_many mm/vmscan.c:4835 [inline]
> > > lru_gen_shrink_node mm/vmscan.c:4935 [inline]
> > > shrink_node+0x3b17/0x4310 mm/vmscan.c:5894
> > > kswapd_shrink_node mm/vmscan.c:6704 [inline]
> > > balance_pgdat mm/vmscan.c:6895 [inline]
> > > kswapd+0x1882/0x38a0 mm/vmscan.c:7164
> > > kthread+0x2f2/0x390 kernel/kthread.c:388
> > > ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
> > > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> > >
> > > -> #0 (fs_reclaim){+.+.}-{0:0}:
> > > check_prev_add kernel/locking/lockdep.c:3134 [inline]
> > > check_prevs_add kernel/locking/lockdep.c:3253 [inline]
> > > validate_chain+0x18cb/0x58e0 kernel/locking/lockdep.c:3869
> > > __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
> > > lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
> > > __fs_reclaim_acquire mm/page_alloc.c:3698 [inline]
> > > fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3712
> > > might_alloc include/linux/sched/mm.h:312 [inline]
> > > slab_pre_alloc_hook mm/slub.c:3746 [inline]
> > > slab_alloc_node mm/slub.c:3827 [inline]
> > > kmalloc_trace+0x47/0x360 mm/slub.c:3992
> > > kmalloc include/linux/slab.h:628 [inline]
> > > add_stack_record_to_list mm/page_owner.c:177 [inline]
> > > inc_stack_record_count mm/page_owner.c:219 [inline]
> > > __set_page_owner+0x561/0x810 mm/page_owner.c:334
> > > set_page_owner include/linux/page_owner.h:32 [inline]
> > > post_alloc_hook+0x1ea/0x210 mm/page_alloc.c:1534
> > > prep_new_page mm/page_alloc.c:1541 [inline]
> > > get_page_from_freelist+0x3410/0x35b0 mm/page_alloc.c:3317
> > > __alloc_pages+0x256/0x6c0 mm/page_alloc.c:4575
> > > __alloc_pages_bulk+0x729/0xd40 mm/page_alloc.c:4523
> > > alloc_pages_bulk_array include/linux/gfp.h:202 [inline]
> > > xfs_buf_alloc_pages+0x1a7/0x860 fs/xfs/xfs_buf.c:398
> > > xfs_buf_find_insert+0x19a/0x1540 fs/xfs/xfs_buf.c:650
> > > xfs_buf_get_map+0x149c/0x1ae0 fs/xfs/xfs_buf.c:755
> > > xfs_buf_read_map+0x111/0xa60 fs/xfs/xfs_buf.c:860
> > > xfs_trans_read_buf_map+0x260/0xad0 fs/xfs/xfs_trans_buf.c:289
> > > xfs_da_read_buf+0x2b1/0x470 fs/xfs/libxfs/xfs_da_btree.c:2674
> > > xfs_dir3_block_read+0x92/0x1a0 fs/xfs/libxfs/xfs_dir2_block.c:145
> > > xfs_dir2_block_lookup_int+0x109/0x7d0 fs/xfs/libxfs/xfs_dir2_block.c:700
> > > xfs_dir2_block_lookup+0x19a/0x630 fs/xfs/libxfs/xfs_dir2_block.c:650
> > > xfs_dir_lookup+0x633/0xaf0 fs/xfs/libxfs/xfs_dir2.c:399
> >
> > Hm. We've taken an ILOCK in xfs_dir_lookup, and now we're reading a
> > directory block. We don't have PF_MEMALLOC_NOFS set, nor do we pass
> > GFP_NOFS when allocating the xfs_buf pages.
> >
> > Nothing in this code path sets PF_MEMALLOC_NOFS explicitly, nor does it
> > create a xfs_trans_alloc_empty, which would set that. Prior to the
> > removal of kmem_alloc, I think we were much more aggressive about
> > GFP_NOFS usage.
>
> This isn't an XFS bug. The XFS code is correct - the callsite in the
> buffer cache is using GFP_KERNEL | __GFP_NOLOCKDEP explicitly to
> avoid these sorts of false positives.
>
> Please take a closer look at the stack trace - there's a second
> memory allocation taking place there way below the XFS memory
> allocation inside the page owner tracking code itself:
>
> static void add_stack_record_to_list(struct stack_record *stack_record,
> gfp_t gfp_mask)
> {
> unsigned long flags;
> struct stack *stack;
>
> /* Filter gfp_mask the same way stackdepot does, for consistency */
> gfp_mask &= ~GFP_ZONEMASK;
> gfp_mask &= (GFP_ATOMIC | GFP_KERNEL);
> gfp_mask |= __GFP_NOWARN;
>
> set_current_in_page_owner();
> stack = kmalloc(sizeof(*stack), gfp_mask);
> if (!stack) {
> unset_current_in_page_owner();
> return;
> }
> unset_current_in_page_owner();
> .....
>
> Look familiar? That exactly the same gfp mask filtering that the
> stackdepot code was doing that caused this issue with KASAN:
>
> https://lore.kernel.org/linux-xfs/000000000000fbf10e06164f3695@google.com/
>
> Which was fixed with this patch:
>
> https://lore.kernel.org/linux-xfs/20240418141133.22950-1-ryabinin.a.a@gmail.com/
>
> Essentially, we're now playing whack-a-mole with internal kernel
> debug code that doesn't honor __GFP_NOLOCKDEP....
>
> MM-people: can you please do an audit of all the nested allocations
> that occur inside the public high level allocation API and ensure
> that they all obey __GFP_NOLOCKDEP so we don't have syzbot keep
> tripping over them one at a time?

Ah. Well. Given my clear inability to investigate these reports
sufficiently, I will step back and let the experts handle them from now
on.

--D

> -Dave.
> --
> Dave Chinner
> david@fromorbit.com
>