Re: [syzbot] [xfs?] possible deadlock in xfs_ilock_data_map_shared

["Darrick J. Wong" <djwong@kernel.org>]

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>
> 
> 
> ---
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