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sunrpc/cache: ensure items removed from cache do not have pending upcalls.

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It is possible for a race to set CACHE_PENDING after cache_clean()
has removed a cache entry from the cache.
If CACHE_PENDING is still set when the entry is finally 'put',
the cache_dequeue() will never happen and we can leak memory.

So set a new flag 'CACHE_CLEANED' when we remove something from
the cache, and don't queue any upcall if it is set.

If CACHE_PENDING is set before CACHE_CLEANED, the call that
cache_clean() makes to cache_fresh_unlocked() will free memory
as needed.  If CACHE_PENDING is set after CACHE_CLEANED, the
test in sunrpc_cache_pipe_upcall will ensure that the memory
is not allocated.

Reported-by: <bstroesser@ts.fujitsu.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
NeilBrown 2013-06-13 12:53:42 +10:00 committed by J. Bruce Fields
parent 2a1c7f53fd
commit 013920eb5d
2 changed files with 6 additions and 1 deletions
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1
include/linux/sunrpc/cache.h
View file

@ -57,6 +57,7 @@ struct cache_head {
#define CACHE_VALID 0 /* Entry contains valid data */
#define CACHE_NEGATIVE 1 /* Negative entry - there is no match for the key */
#define CACHE_PENDING 2 /* An upcall has been sent but no reply received yet*/
#define CACHE_CLEANED 3 /* Entry has been cleaned from cache */
#define CACHE_NEW_EXPIRY 120 /* keep new things pending confirmation for 120 seconds */

6
net/sunrpc/cache.c
View file

@ -306,7 +306,7 @@ EXPORT_SYMBOL_GPL(cache_check);
* a current pointer into that list and into the table
* for that entry.
*
* Each time clean_cache is called it finds the next non-empty entry
* Each time cache_clean is called it finds the next non-empty entry
* in the current table and walks the list in that entry
* looking for entries that can be removed.
*
@ -453,6 +453,7 @@ static int cache_clean(void)
current_index ++;
spin_unlock(&cache_list_lock);
if (ch) {
set_bit(CACHE_CLEANED, &ch->flags);
cache_fresh_unlocked(ch, d);
cache_put(ch, d);
}
@ -1178,6 +1179,9 @@ int sunrpc_cache_pipe_upcall(struct cache_detail *detail, struct cache_head *h)
warn_no_listener(detail);
return -EINVAL;
}
if (test_bit(CACHE_CLEANED, &h->flags))
/* Too late to make an upcall */
return -EAGAIN;
buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (!buf)