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ubik: Fix buffers for reading-during-writes

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If we are reading while a write transaction is in progress, we can
encounter a buffer that is dirty if we're on the same site as the
writer. Ignore these buffers for readers, since they contain
uncommitted changes. Then, when the writer commits, invalidate the
resultant duplicate buffer, if one exists.

Change-Id: I67e0205362d4c08ea9a8c12104fea8bfe8cbf798
Reviewed-on: http://gerrit.openafs.org/2231
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
This commit is contained in:
Andrew Deason 2010-06-22 14:36:42 -05:00 committed by Derrick Brashear
parent 5c7297a6c7
commit 570236dd55
1 changed files with 30 additions and 1 deletions
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31
src/ubik/disk.c
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@ -326,6 +326,12 @@ MatchBuffer(struct buffer *buf, int page, afs_int32 fid,
if (buf->file != fid) {
return 0;
}
if (atrans->type == UBIK_READTRANS && buf->dirty) {
/* if 'buf' is dirty, it has uncommitted changes; we do not want to
* see uncommitted changes if we are a read transaction, so skip over
* it. */
return 0;
}
if (buf->dbase != atrans->dbase) {
return 0;
}
@ -624,6 +630,27 @@ DAbort(struct ubik_trans *atrans)
return 0;
}
/**
* Invalidate any buffers that are duplicates of abuf. Duplicate buffers
* can appear if a read transaction reads a page that is dirty, then that
* dirty page is synced. The read transaction will skip over the dirty page,
* and create a new buffer, and when the dirty page is synced, it will be
* identical (except for contents) to the read-transaction buffer.
*/
static void
DedupBuffer(struct buffer *abuf)
{
struct buffer *tb;
for (tb = phTable[pHash(abuf->page)]; tb; tb = tb->hashNext) {
if (tb->page == abuf->page && tb != abuf && tb->file == abuf->file
&& tb->dbase == abuf->dbase) {
tb->file = BADFID;
Dlru(tb);
}
}
}
/*!
* \attention DSync() must only be called after DFlush(), due to its interpretation of dirty flag.
*/
@ -644,8 +671,10 @@ DSync(struct ubik_trans *atrans)
if (tb->dirty == 1) {
if (file == BADFID)
file = tb->file;
if (file != BADFID && tb->file == file)
if (file != BADFID && tb->file == file) {
tb->dirty = 0;
DedupBuffer(tb);
}
}
}
if (file == BADFID)