6.12-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
commit da2dccd7451de62b175fb8f0808d644959e964c7 upstream.
At btrfs_write_check() if our file's i_size is not sector size aligned and we have a write that starts at an offset larger than the i_size that falls within the same page of the i_size, then we end up not zeroing the file range [i_size, write_offset).
The code is this:
start_pos = round_down(pos, fs_info->sectorsize); oldsize = i_size_read(inode); if (start_pos > oldsize) { /* Expand hole size to cover write data, preventing empty gap */ loff_t end_pos = round_up(pos + count, fs_info->sectorsize);
ret = btrfs_cont_expand(BTRFS_I(inode), oldsize, end_pos); if (ret) return ret; }
So if our file's i_size is 90269 bytes and a write at offset 90365 bytes comes in, we get 'start_pos' set to 90112 bytes, which is less than the i_size and therefore we don't zero out the range [90269, 90365) by calling btrfs_cont_expand().
This is an old bug introduced in commit 9036c10208e1 ("Btrfs: update hole handling v2"), from 2008, and the buggy code got moved around over the years.
Fix this by discarding 'start_pos' and comparing against the write offset ('pos') without any alignment.
This bug was recently exposed by test case generic/363 which tests this scenario by polluting ranges beyond EOF with an mmap write and than verify that after a file increases we get zeroes for the range which is supposed to be a hole and not what we wrote with the previous mmaped write.
We're only seeing this exposed now because generic/363 used to run only on xfs until last Sunday's fstests update.
The test was failing like this:
$ ./check generic/363 FSTYP -- btrfs PLATFORM -- Linux/x86_64 debian0 6.13.0-rc7-btrfs-next-185+ #17 SMP PREEMPT_DYNAMIC Mon Feb 3 12:28:46 WET 2025 MKFS_OPTIONS -- /dev/sdc MOUNT_OPTIONS -- /dev/sdc /home/fdmanana/btrfs-tests/scratch_1
generic/363 0s ... [failed, exit status 1]- output mismatch (see /home/fdmanana/git/hub/xfstests/results//generic/363.out.bad) # --- tests/generic/363.out 2025-02-05 15:31:14.013646509 +0000 # +++ /home/fdmanana/git/hub/xfstests/results//generic/363.out.bad 2025-02-05 17:25:33.112630781 +0000 @@ -1 +1,46 @@ QA output created by 363 +READ BAD DATA: offset = 0xdcad, size = 0xd921, fname = /home/fdmanana/btrfs-tests/dev/junk +OFFSET GOOD BAD RANGE +0x1609d 0x0000 0x3104 0x0 +operation# (mod 256) for the bad data may be 4 +0x1609e 0x0000 0x0472 0x1 +operation# (mod 256) for the bad data may be 4 ... (Run 'diff -u /home/fdmanana/git/hub/xfstests/tests/generic/363.out /home/fdmanana/git/hub/xfstests/results//generic/363.out.bad' to see the entire diff) Ran: generic/363 Failures: generic/363 Failed 1 of 1 tests
Fixes: 9036c10208e1 ("Btrfs: update hole handling v2") CC: stable@vger.kernel.org Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/file.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1148,7 +1148,6 @@ int btrfs_write_check(struct kiocb *iocb loff_t pos = iocb->ki_pos; int ret; loff_t oldsize; - loff_t start_pos;
/* * Quickly bail out on NOWAIT writes if we don't have the nodatacow or @@ -1172,9 +1171,8 @@ int btrfs_write_check(struct kiocb *iocb */ update_time_for_write(inode);
- start_pos = round_down(pos, fs_info->sectorsize); oldsize = i_size_read(inode); - if (start_pos > oldsize) { + if (pos > oldsize) { /* Expand hole size to cover write data, preventing empty gap */ loff_t end_pos = round_up(pos + count, fs_info->sectorsize);