On Wed, 2008-04-30 at 06:41 +0000, Clay McClure wrote: > Hello, > > When multiple 2.6.18 NFSv3 clients write to the same file, after one of the > clients has recently read from the file, we see data corruption in the form of > null bytes inserted into the file. > > Simple test case: > > hosta% echo "line 1" > /nfs/volume/bar.txt > > then, in rapid succession: > > hostb% cat bar.txt && sleep 2 && echo "line 2 from hostb" >> /nfs/bar.txt > hostc% cat bar.txt && sleep 2 && echo "line 2 from hostc" >> /nfs/bar.txt > > Expected result: > > /nfs/bar.txt contains: > > line 1 > line 2 from hostb > line 2 from hostc > > Actual result: > > /nfs/bar.txt contains: > > line 1 > \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0line 2 from hostc > > This seems to be due to an inconsistency between the page cache and the > attribute cache on hostc. Running the 'cat' command on hostc causes bar.txt > to be loaded into the page cache. Meanwhile, its attributes are cached in the > attribute cache. > > Seconds later, the 'echo' command on hostc causes the attribute cache to be > updated (a GETATTR operation is issued) with the new file size (reflecting > the line just appended by hostb), but the page cache is not updated (no READ > operation is issued). > > The subsequent WRITE operation from hostc specifies an offset of 0 (beginning > of file) and a length equal to "line 1" + "line 2 from hostb" + "line 2 from > hostc". Since the page cache on hostc does not contain the "line 2 from hostb" > content, that segment of the WRITE buffer is filled with nulls. > > Note that no file locking is being used in this test case or our production > use case. > > Questions: > > - Is this a bug or correct operation? > - Would file locking produce the expected behaviour? > > Thanks, > > Clay McClure A number of read and write races have been fixed since September 2006. Have you tested with 2.6.25? Trond -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
