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 b778cf962d71a0e737923d55d0432f3bd287258e Mon Sep 17 00:00:00 2001

From: Josef Bacik josef@toxicpanda.com Date: Thu, 13 Feb 2020 10:47:31 -0500 Subject: [PATCH] btrfs: fix bytes_may_use underflow in prealloc error condtition

I hit the following warning while running my error injection stress testing:

WARNING: CPU: 3 PID: 1453 at fs/btrfs/space-info.h:108 btrfs_free_reserved_data_space_noquota+0xfd/0x160 [btrfs] RIP: 0010:btrfs_free_reserved_data_space_noquota+0xfd/0x160 [btrfs] Call Trace: btrfs_free_reserved_data_space+0x4f/0x70 [btrfs] __btrfs_prealloc_file_range+0x378/0x470 [btrfs] elfcorehdr_read+0x40/0x40 ? elfcorehdr_read+0x40/0x40 ? btrfs_commit_transaction+0xca/0xa50 [btrfs] ? dput+0xb4/0x2a0 ? btrfs_log_dentry_safe+0x55/0x70 [btrfs] ? btrfs_sync_file+0x30e/0x420 [btrfs] ? do_fsync+0x38/0x70 ? __x64_sys_fdatasync+0x13/0x20 ? do_syscall_64+0x5b/0x1b0 ? entry_SYSCALL_64_after_hwframe+0x44/0xa9

This happens if we fail to insert our reserved file extent. At this point we've already converted our reservation from ->bytes_may_use to ->bytes_reserved. However once we break we will attempt to free everything from [cur_offset, end] from ->bytes_may_use, but our extent reservation will overlap part of this.

Fix this problem by adding ins.offset (our extent allocation size) to cur_offset so we remove the actual remaining part from ->bytes_may_use.

I validated this fix using my inject-error.py script

python inject-error.py -o should_fail_bio -t cache_save_setup -t \ __btrfs_prealloc_file_range \ -t insert_reserved_file_extent.constprop.0 \ -r "-5" ./run-fsstress.sh

where run-fsstress.sh simply mounts and runs fsstress on a disk.

CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Qu Wenruo wqu@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/inode.c b/fs/btrfs/inode.c index 36deef69f847..4f47ba652b31 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -9824,6 +9824,7 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, struct btrfs_root *root = BTRFS_I(inode)->root; struct btrfs_key ins; u64 cur_offset = start; + u64 clear_offset = start; u64 i_size; u64 cur_bytes; u64 last_alloc = (u64)-1; @@ -9858,6 +9859,15 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, btrfs_end_transaction(trans); break; } + + /* + * We've reserved this space, and thus converted it from + * ->bytes_may_use to ->bytes_reserved. Any error that happens + * from here on out we will only need to clear our reservation + * for the remaining unreserved area, so advance our + * clear_offset by our extent size. + */ + clear_offset += ins.offset; btrfs_dec_block_group_reservations(fs_info, ins.objectid);

last_alloc = ins.offset; @@ -9937,9 +9947,9 @@ static int __btrfs_prealloc_file_range(struct inode *inode, int mode, if (own_trans) btrfs_end_transaction(trans); } - if (cur_offset < end) - btrfs_free_reserved_data_space(inode, NULL, cur_offset, - end - cur_offset + 1); + if (clear_offset < end) + btrfs_free_reserved_data_space(inode, NULL, clear_offset, + end - clear_offset + 1); return ret; }