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| author | Brian Foster <bfoster@redhat.com> | 2022-11-30 08:41:01 -0800 |
|---|---|---|
| committer | Darrick J. Wong <djwong@kernel.org> | 2022-11-30 08:41:01 -0800 |
| commit | a79168a0c00d710420c1758f6c38df89e12f0763 (patch) | |
| tree | f9a7d9faade51d699ff87f3aed8bf281ab19785b /fs/remap_range.c | |
| parent | f0c4d9fc9cc9462659728d168387191387e903cc (diff) | |
| download | linux-a79168a0c00d710420c1758f6c38df89e12f0763.tar.gz | |
fs/remap_range: avoid spurious writeback on zero length request
generic_remap_checks() can reduce the effective request length (i.e.,
after the reflink extend to EOF case is handled) down to zero. If this
occurs, __generic_remap_file_range_prep() proceeds through dio
serialization, file mapping flush calls, and may invoke file_modified()
before returning back to the filesystem caller, all of which immediately
check for len == 0 and return.
While this is mostly harmless, it is spurious and not completely
without side effect. A filemap write call can submit I/O (but not
wait on it) when the specified end byte precedes the start but
happens to land on the same aligned page boundary, which can occur
from __generic_remap_file_range_prep() when len is 0.
The dedupe path already has a len == 0 check to break out before
doing range comparisons. Lift this check a bit earlier in the
function to cover the general case of len == 0 and avoid the
unnecessary work. While here, account for the case where
generic_remap_check_len() may also reduce length to zero.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Diffstat (limited to 'fs/remap_range.c')
| -rw-r--r-- | fs/remap_range.c | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/fs/remap_range.c b/fs/remap_range.c index 654912d068622..8741ecd616a7a 100644 --- a/fs/remap_range.c +++ b/fs/remap_range.c @@ -304,7 +304,7 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in, /* Check that we don't violate system file offset limits. */ ret = generic_remap_checks(file_in, pos_in, file_out, pos_out, len, remap_flags); - if (ret) + if (ret || *len == 0) return ret; /* Wait for the completion of any pending IOs on both files */ @@ -328,9 +328,6 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in, if (remap_flags & REMAP_FILE_DEDUP) { bool is_same = false; - if (*len == 0) - return 0; - if (!IS_DAX(inode_in)) ret = vfs_dedupe_file_range_compare(file_in, pos_in, file_out, pos_out, *len, &is_same); @@ -348,7 +345,7 @@ __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in, ret = generic_remap_check_len(inode_in, inode_out, pos_out, len, remap_flags); - if (ret) + if (ret || *len == 0) return ret; /* If can't alter the file contents, we're done. */ |