From: Josef Bacik josef@toxicpanda.com
commit 597441b3436a43011f31ce71dc0a6c0bf5ce958a upstream.
Our CI system caught a lockdep splat:
====================================================== WARNING: possible circular locking dependency detected 6.3.0-rc7+ #1167 Not tainted ------------------------------------------------------ kswapd0/46 is trying to acquire lock: ffff8c6543abd650 (sb_internal#2){++++}-{0:0}, at: btrfs_commit_inode_delayed_inode+0x5f/0x120
but task is already holding lock: ffffffffabe61b40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x4aa/0x7a0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (fs_reclaim){+.+.}-{0:0}: fs_reclaim_acquire+0xa5/0xe0 kmem_cache_alloc+0x31/0x2c0 alloc_extent_state+0x1d/0xd0 __clear_extent_bit+0x2e0/0x4f0 try_release_extent_mapping+0x216/0x280 btrfs_release_folio+0x2e/0x90 invalidate_inode_pages2_range+0x397/0x470 btrfs_cleanup_dirty_bgs+0x9e/0x210 btrfs_cleanup_one_transaction+0x22/0x760 btrfs_commit_transaction+0x3b7/0x13a0 create_subvol+0x59b/0x970 btrfs_mksubvol+0x435/0x4f0 __btrfs_ioctl_snap_create+0x11e/0x1b0 btrfs_ioctl_snap_create_v2+0xbf/0x140 btrfs_ioctl+0xa45/0x28f0 __x64_sys_ioctl+0x88/0xc0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc
-> #0 (sb_internal#2){++++}-{0:0}: __lock_acquire+0x1435/0x21a0 lock_acquire+0xc2/0x2b0 start_transaction+0x401/0x730 btrfs_commit_inode_delayed_inode+0x5f/0x120 btrfs_evict_inode+0x292/0x3d0 evict+0xcc/0x1d0 inode_lru_isolate+0x14d/0x1e0 __list_lru_walk_one+0xbe/0x1c0 list_lru_walk_one+0x58/0x80 prune_icache_sb+0x39/0x60 super_cache_scan+0x161/0x1f0 do_shrink_slab+0x163/0x340 shrink_slab+0x1d3/0x290 shrink_node+0x300/0x720 balance_pgdat+0x35c/0x7a0 kswapd+0x205/0x410 kthread+0xf0/0x120 ret_from_fork+0x29/0x50
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(sb_internal#2); lock(fs_reclaim); lock(sb_internal#2);
*** DEADLOCK ***
3 locks held by kswapd0/46: #0: ffffffffabe61b40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x4aa/0x7a0 #1: ffffffffabe50270 (shrinker_rwsem){++++}-{3:3}, at: shrink_slab+0x113/0x290 #2: ffff8c6543abd0e0 (&type->s_umount_key#44){++++}-{3:3}, at: super_cache_scan+0x38/0x1f0
stack backtrace: CPU: 0 PID: 46 Comm: kswapd0 Not tainted 6.3.0-rc7+ #1167 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x58/0x90 check_noncircular+0xd6/0x100 ? save_trace+0x3f/0x310 ? add_lock_to_list+0x97/0x120 __lock_acquire+0x1435/0x21a0 lock_acquire+0xc2/0x2b0 ? btrfs_commit_inode_delayed_inode+0x5f/0x120 start_transaction+0x401/0x730 ? btrfs_commit_inode_delayed_inode+0x5f/0x120 btrfs_commit_inode_delayed_inode+0x5f/0x120 btrfs_evict_inode+0x292/0x3d0 ? lock_release+0x134/0x270 ? __pfx_wake_bit_function+0x10/0x10 evict+0xcc/0x1d0 inode_lru_isolate+0x14d/0x1e0 __list_lru_walk_one+0xbe/0x1c0 ? __pfx_inode_lru_isolate+0x10/0x10 ? __pfx_inode_lru_isolate+0x10/0x10 list_lru_walk_one+0x58/0x80 prune_icache_sb+0x39/0x60 super_cache_scan+0x161/0x1f0 do_shrink_slab+0x163/0x340 shrink_slab+0x1d3/0x290 shrink_node+0x300/0x720 balance_pgdat+0x35c/0x7a0 kswapd+0x205/0x410 ? __pfx_autoremove_wake_function+0x10/0x10 ? __pfx_kswapd+0x10/0x10 kthread+0xf0/0x120 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x29/0x50 </TASK>
This happens because when we abort the transaction in the transaction commit path we call invalidate_inode_pages2_range on our block group cache inodes (if we have space cache v1) and any delalloc inodes we may have. The plain invalidate_inode_pages2_range() call passes through GFP_KERNEL, which makes sense in most cases, but not here. Wrap these two invalidate callees with memalloc_nofs_save/memalloc_nofs_restore to make sure we don't end up with the fs reclaim dependency under the transaction dependency.
CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/disk-io.c | 9 +++++++++ 1 file changed, 9 insertions(+)
--- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -4796,7 +4796,11 @@ static void btrfs_destroy_delalloc_inode */ inode = igrab(&btrfs_inode->vfs_inode); if (inode) { + unsigned int nofs_flag; + + nofs_flag = memalloc_nofs_save(); invalidate_inode_pages2(inode->i_mapping); + memalloc_nofs_restore(nofs_flag); iput(inode); } spin_lock(&root->delalloc_lock); @@ -4901,7 +4905,12 @@ static void btrfs_cleanup_bg_io(struct b
inode = cache->io_ctl.inode; if (inode) { + unsigned int nofs_flag; + + nofs_flag = memalloc_nofs_save(); invalidate_inode_pages2(inode->i_mapping); + memalloc_nofs_restore(nofs_flag); + BTRFS_I(inode)->generation = 0; cache->io_ctl.inode = NULL; iput(inode);