The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 572c83acdcdafeb04e70aa46be1fa539310be20c Mon Sep 17 00:00:00 2001

From: Josef Bacik josef@toxicpanda.com Date: Tue, 29 Sep 2020 08:53:54 -0400 Subject: [PATCH] btrfs: cleanup cow block on error

In fstest btrfs/064 a transaction abort in __btrfs_cow_block could lead to a system lockup. It gets stuck trying to write back inodes, and the write back thread was trying to lock an extent buffer:

$ cat /proc/2143497/stack [<0>] __btrfs_tree_lock+0x108/0x250 [<0>] lock_extent_buffer_for_io+0x35e/0x3a0 [<0>] btree_write_cache_pages+0x15a/0x3b0 [<0>] do_writepages+0x28/0xb0 [<0>] __writeback_single_inode+0x54/0x5c0 [<0>] writeback_sb_inodes+0x1e8/0x510 [<0>] wb_writeback+0xcc/0x440 [<0>] wb_workfn+0xd7/0x650 [<0>] process_one_work+0x236/0x560 [<0>] worker_thread+0x55/0x3c0 [<0>] kthread+0x13a/0x150 [<0>] ret_from_fork+0x1f/0x30

This is because we got an error while COWing a block, specifically here

if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state)) { ret = btrfs_reloc_cow_block(trans, root, buf, cow); if (ret) { btrfs_abort_transaction(trans, ret); return ret; } }

[16402.241552] BTRFS: Transaction aborted (error -2) [16402.242362] WARNING: CPU: 1 PID: 2563188 at fs/btrfs/ctree.c:1074 __btrfs_cow_block+0x376/0x540 [16402.249469] CPU: 1 PID: 2563188 Comm: fsstress Not tainted 5.9.0-rc6+ #8 [16402.249936] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 [16402.250525] RIP: 0010:__btrfs_cow_block+0x376/0x540 [16402.252417] RSP: 0018:ffff9cca40e578b0 EFLAGS: 00010282 [16402.252787] RAX: 0000000000000025 RBX: 0000000000000002 RCX: ffff9132bbd19388 [16402.253278] RDX: 00000000ffffffd8 RSI: 0000000000000027 RDI: ffff9132bbd19380 [16402.254063] RBP: ffff9132b41a49c0 R08: 0000000000000000 R09: 0000000000000000 [16402.254887] R10: 0000000000000000 R11: ffff91324758b080 R12: ffff91326ef17ce0 [16402.255694] R13: ffff91325fc0f000 R14: ffff91326ef176b0 R15: ffff9132815e2000 [16402.256321] FS: 00007f542c6d7b80(0000) GS:ffff9132bbd00000(0000) knlGS:0000000000000000 [16402.256973] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [16402.257374] CR2: 00007f127b83f250 CR3: 0000000133480002 CR4: 0000000000370ee0 [16402.257867] Call Trace: [16402.258072] btrfs_cow_block+0x109/0x230 [16402.258356] btrfs_search_slot+0x530/0x9d0 [16402.258655] btrfs_lookup_file_extent+0x37/0x40 [16402.259155] __btrfs_drop_extents+0x13c/0xd60 [16402.259628] ? btrfs_block_rsv_migrate+0x4f/0xb0 [16402.259949] btrfs_replace_file_extents+0x190/0x820 [16402.260873] btrfs_clone+0x9ae/0xc00 [16402.261139] btrfs_extent_same_range+0x66/0x90 [16402.261771] btrfs_remap_file_range+0x353/0x3b1 [16402.262333] vfs_dedupe_file_range_one.part.0+0xd5/0x140 [16402.262821] vfs_dedupe_file_range+0x189/0x220 [16402.263150] do_vfs_ioctl+0x552/0x700 [16402.263662] __x64_sys_ioctl+0x62/0xb0 [16402.264023] do_syscall_64+0x33/0x40 [16402.264364] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [16402.264862] RIP: 0033:0x7f542c7d15cb [16402.266901] RSP: 002b:00007ffd35944ea8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [16402.267627] RAX: ffffffffffffffda RBX: 00000000009d1968 RCX: 00007f542c7d15cb [16402.268298] RDX: 00000000009d2490 RSI: 00000000c0189436 RDI: 0000000000000003 [16402.268958] RBP: 00000000009d2520 R08: 0000000000000036 R09: 00000000009d2e64 [16402.269726] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002 [16402.270659] R13: 000000000001f000 R14: 00000000009d1970 R15: 00000000009d2e80 [16402.271498] irq event stamp: 0 [16402.271846] hardirqs last enabled at (0): [<0000000000000000>] 0x0 [16402.272497] hardirqs last disabled at (0): [<ffffffff910dbf59>] copy_process+0x6b9/0x1ba0 [16402.273343] softirqs last enabled at (0): [<ffffffff910dbf59>] copy_process+0x6b9/0x1ba0 [16402.273905] softirqs last disabled at (0): [<0000000000000000>] 0x0 [16402.274338] ---[ end trace 737874a5a41a8236 ]--- [16402.274669] BTRFS: error (device dm-9) in __btrfs_cow_block:1074: errno=-2 No such entry [16402.276179] BTRFS info (device dm-9): forced readonly [16402.277046] BTRFS: error (device dm-9) in btrfs_replace_file_extents:2723: errno=-2 No such entry [16402.278744] BTRFS: error (device dm-9) in __btrfs_cow_block:1074: errno=-2 No such entry [16402.279968] BTRFS: error (device dm-9) in __btrfs_cow_block:1074: errno=-2 No such entry [16402.280582] BTRFS info (device dm-9): balance: ended with status: -30

The problem here is that as soon as we allocate the new block it is locked and marked dirty in the btree inode. This means that we could attempt to writeback this block and need to lock the extent buffer. However we're not unlocking it here and thus we deadlock.

Fix this by unlocking the cow block if we have any errors inside of __btrfs_cow_block, and also free it so we do not leak it.

CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index a165093739c4..113da62dc17f 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -1064,6 +1064,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans,

ret = update_ref_for_cow(trans, root, buf, cow, &last_ref); if (ret) { + btrfs_tree_unlock(cow); + free_extent_buffer(cow); btrfs_abort_transaction(trans, ret); return ret; } @@ -1071,6 +1073,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, if (test_bit(BTRFS_ROOT_SHAREABLE, &root->state)) { ret = btrfs_reloc_cow_block(trans, root, buf, cow); if (ret) { + btrfs_tree_unlock(cow); + free_extent_buffer(cow); btrfs_abort_transaction(trans, ret); return ret; } @@ -1103,6 +1107,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, if (last_ref) { ret = tree_mod_log_free_eb(buf); if (ret) { + btrfs_tree_unlock(cow); + free_extent_buffer(cow); btrfs_abort_transaction(trans, ret); return ret; }