On Mon, 10 Dec 2012 14:42:23 +0000 "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote: > On Mon, 2012-12-10 at 09:25 -0500, Jeff Layton wrote: > > Jian reported that the following sequence would leave "testfile" with > > corrupt data: > > > > # mount localhost:/export /mnt/nfs/ -o vers=3 > > # echo abc > /mnt/nfs/testfile; echo def >> /export/testfile; echo ghi >> /mnt/nfs/testfile > > # cat -v /export/testfile > > abc > > ^@^@^@^@ghi > > > > While there's no locking involved here, the operations are serialized, > > so CTO should prevent corruption. > > > > The first write to the file is fine and writes 4 bytes. The file is then > > extended on the server. When it's reopened a GETATTR is issued and the > > size change is noticed. This causes NFS_INO_INVALID_DATA to be set on > > the file. Because the file is opened for write only, > > nfs_want_read_modify_write() returns 0 to nfs_write_begin(). > > nfs_updatepage then calls nfs_write_pageuptodate() to see if it should > > extend the nfs_page to cover the whole page. NFS_INO_INVALID_DATA is > > still set on the file at that point, but that flag is ignored and > > nfs_pageuptodate erroneously extends the write to cover the whole page, > > with the write done on the server side filled in with zeroes. > > > > This patch just has that function check for NFS_INO_INVALID_DATA in > > addition to NFS_INO_REVAL_PAGECACHE. This fixes the bug, but looking > > over the code, I wonder if we might have a similar bug in > > nfs_revalidate_size(). The difference between those two flags is very > > subtle, so it seems like we ought to be checking for > > NFS_INO_INVALID_DATA in most of the places that we look for > > NFS_INO_REVAL_PAGECACHE. > > > > I believe this is regression introduced by commit 8d197a568. The code > > did check for NFS_INO_INVALID_DATA prior to that patch. > > > > Original bug report is here: > > > > https://bugzilla.redhat.com/show_bug.cgi?id=885743 > > Hi Jeff, > > The point of NFS_INO_REVAL_PAGECACHE is to be able to distinguish > between situations where the file size or change attribute is in doubt > (and so the page cache validity is in doubt), and situations where other > attributes are in doubt (such as ACCESS caches, file owner, nlinks,...). > This is why we're only checking for NFS_INO_REVAL_PAGECACHE and not > NFS_INO_INVALID_DATA in the functions you mention above. > Ok, now I'm really confused... I thought that: NFS_INO_INVALID_DATA == pagecache data was known to be wrong NFS_INO_REVAL_PAGECACHE == pagecache data is questionable ...but if I understand what you're saying above, the "data" that NFS_INO_INVALID_DATA refers to is in peripheral caches, like the ACCESS cache? I guess then I don't quite understand what NFS_INO_INVALID_ATTR and NFS_INO_INVALID_ACCESS are for. Aren't they supposed to indicate that the attrs and access caches are invalid? > So the fix here should be to set NFS_INO_REVAL_PAGECACHE when the change > attribute and/or size change is noticed. The only function I can see > that appears to get this wrong is nfs_wcc_update_inode(). Does fixing > that lay the bug to rest? > No, that doesn't fix it. There's another place that misses setting that flag too in nfs_update_inode() where the size changes. I added it there too and that also didn't fix it. Here's why (I think): When the size change is noticed via the CTO GETATTR call, then my patched kernel now sets NFS_INO_REVAL_PAGECACHE in nfs_update_inode. Now cache_validity is set to 0x2a. The kernel then makes an ACCESS call that also ultimately ends up in nfs_update_inode. nfs_update_inode saves off the cache_validity flags and clears all of them except for NFS_INO_INVALID_DATA. As best I can tell, the saved_cache_validity is then ending up discarded and on exit the cache_validity is ending up set to just NFS_INO_INVALID_DATA. It seems like we ought to be restoring the save_cache_validity flags before exiting that function, but I confess that I don't quite grasp the logic in nfs_update_inode. Thoughts? -- Jeff Layton <jlayton@xxxxxxxxxx> -- 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
