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Dave Chinner authored
After a fair number of xfstests runs, xfs/182 started to fail regularly with a corrupted directory - a directory read verifier was failing after recovery because it found a block with a XARM magic number (remote attribute block) rather than a directory data block. The first time I saw this repeated failure I did /something/ and the problem went away, so I was never able to find the underlying problem. Test xfs/182 failed again today, and I found the root cause before I did /something else/ that made it go away. Tracing indicated that the block in question was being correctly logged, the log was being flushed by sync, but the buffer was not being written back before the shutdown occurred. Tracing also indicated that log recovery was also reading the block, but then never writing it before log recovery invalidated the cache, indicating that it was not modified by log recovery. More detailed analysis of the corpse indicated that the filesystem had a uuid of "a4131074-1872-4cac-9323-2229adbcb886" but the XARM block had a uuid of "8f32f043-c3c9-e7f8-f947-4e7f989c05d3", which indicated it was a block from an older filesystem. The reason that log recovery didn't replay it was that the LSN in the XARM block was larger than the LSN of the transaction being replayed, and so the block was not overwritten by log recovery. Hence, log recovery cant blindly trust the magic number and LSN in the block - it must verify that it belongs to the filesystem being recovered before using the LSN. i.e. if the UUIDs don't match, we need to unconditionally recovery the change held in the log. This patch was first tested on a block device that was repeatedly causing xfs/182 to fail with the same failure on the same block with the same directory read corruption signature (i.e. XARM block). It did not fail, and hasn't failed since. Signed-off-by:
Dave Chinner <dchinner@redhat.com> Reviewed-by:
Ben Myers <bpm@sgi.com> Signed-off-by:
Ben Myers <bpm@sgi.com>
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