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

From: Darrick J. Wong
Date: Fri Apr 26 2024 - 19:17:26 EST

On Sat, Apr 27, 2024 at 07:20:03AM +1000, Dave Chinner wrote:
> [cc linux-mm@xxxxxxxxx]
>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > 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@xxxxxxxxxx/
>
> Which was fixed with this patch:
>
> https://lore.kernel.org/linux-xfs/20240418141133.22950-1-ryabinin.a.a@xxxxxxxxx/
>
> 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@xxxxxxxxxxxxx
>