diff options
author | J. Bruce Fields <bfields@redhat.com> | 2011-01-04 14:12:47 -0500 |
---|---|---|
committer | J. Bruce Fields <bfields@redhat.com> | 2011-01-04 16:49:25 -0500 |
commit | fdef7aa5d4020fd94ffcbf0078d6bd9e5a111e19 (patch) | |
tree | 270c2b03e9cb5cf5451b0e229c5a328727ef743a /net | |
parent | 6bab93f87ec703bf6650875881b11f9f27d7da56 (diff) |
svcrpc: ensure cache_check caller sees updated entry
Supposes cache_check runs simultaneously with an update on a different
CPU:
cache_check task doing update
^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^
1. test for CACHE_VALID 1'. set entry->data
& !CACHE_NEGATIVE
2. use entry->data 2'. set CACHE_VALID
If the two memory writes performed in step 1' and 2' appear misordered
with respect to the reads in step 1 and 2, then the caller could get
stale data at step 2 even though it saw CACHE_VALID set on the cache
entry.
Add memory barriers to prevent this.
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Diffstat (limited to 'net')
-rw-r--r-- | net/sunrpc/cache.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index a6c57334fa13..72ad836e4fe0 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -128,6 +128,7 @@ static void cache_fresh_locked(struct cache_head *head, time_t expiry) { head->expiry_time = expiry; head->last_refresh = seconds_since_boot(); + smp_wmb(); /* paired with smp_rmb() in cache_is_valid() */ set_bit(CACHE_VALID, &head->flags); } @@ -208,8 +209,16 @@ static inline int cache_is_valid(struct cache_detail *detail, struct cache_head /* entry is valid */ if (test_bit(CACHE_NEGATIVE, &h->flags)) return -ENOENT; - else + else { + /* + * In combination with write barrier in + * sunrpc_cache_update, ensures that anyone + * using the cache entry after this sees the + * updated contents: + */ + smp_rmb(); return 0; + } } } |