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Block cache use rht _lookup_ insert for EEXIST

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The sneaky rhashtable_insert_fast() can't return -EEXIST despite the
last line of the function *REALLY* making it look like it can.  It just
inserts new objects at the head of the bucket lists without comparing
the insertion with existing objects.

The block cache was relying on insertion to resolve duplicate racing
allocated blocks.  Because it couldn't return -EEXIST we could get
duplicate cached blocks present in the hash table.

rhashtable_lookup_insert_fast() fixes this by actually comparing the
inserted objects key with the objects found in the insertion bucket.  A
racing allocator trying to insert a duplicate cached block will get an
error, drop their allocated block, and retry their lookup.

Signed-off-by: Zach Brown <zab@versity.com>
This commit is contained in:
Zach Brown
2021-04-07 14:34:05 -07:00
parent cf3cb3f197
commit c3290771a0
1 changed files with 1 additions and 1 deletions
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2
kmod/src/block.c
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@@ -288,7 +288,7 @@ static int block_insert(struct super_block *sb, struct block_private *bp)
retry:
atomic_add(BLOCK_REF_INSERTED, &bp->refcount);
ret = rhashtable_insert_fast(&binf->ht, &bp->ht_head, block_ht_params);
ret = rhashtable_lookup_insert_fast(&binf->ht, &bp->ht_head, block_ht_params);
if (ret < 0) {
atomic_sub(BLOCK_REF_INSERTED, &bp->refcount);
if (ret == -EBUSY) {