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inet: frag: don't re-use chainlist for evictor 

commit 65ba1f1ec0 ("inet: frags: fix a race between inet_evict_bucket
and inet_frag_kill") describes the bug, but the fix doesn't work reliably.

Problem is that ->flags member can be set on other cpu without chainlock
being held by that task, i.e. the RMW-Cycle can clear INET_FRAG_EVICTED
bit after we put the element on the evictor private list.

We can crash when walking the 'private' evictor list since an element can
be deleted from list underneath the evictor.

Join work with Nikolay Alexandrov.

Fixes: b13d3cbfb8 ("inet: frag: move eviction of queues to work queue")
Reported-by: Johan Schuijt <johan@transip.nl>
Tested-by: Frank Schreuder <fschreuder@transip.nl>
Signed-off-by: Nikolay Alexandrov <nikolay@cumulusnetworks.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2015-07-23 12:05:37 +02:00 committed by David S. Miller
parent 81296fc673
commit d1fe19444d
2 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/inet_frag.h
View File

@ -45,6 +45,7 @@ enum {
* @flags: fragment queue flags * @flags: fragment queue flags
* @max_size: maximum received fragment size * @max_size: maximum received fragment size
* @net: namespace that this frag belongs to * @net: namespace that this frag belongs to
* @list_evictor: list of queues to forcefully evict (e.g. due to low memory)
*/ */
struct inet_frag_queue { struct inet_frag_queue {
spinlock_t lock; spinlock_t lock;
@ -59,6 +60,7 @@ struct inet_frag_queue {
__u8 flags; __u8 flags;
u16 max_size; u16 max_size;
struct netns_frags *net; struct netns_frags *net;
struct hlist_node list_evictor;
}; };
#define INETFRAGS_HASHSZ 1024 #define INETFRAGS_HASHSZ 1024

8
net/ipv4/inet_fragment.c
View File

@ -151,14 +151,13 @@ evict_again:
} }
fq->flags |= INET_FRAG_EVICTED; fq->flags |= INET_FRAG_EVICTED;
hlist_del(&fq->list); hlist_add_head(&fq->list_evictor, &expired);
hlist_add_head(&fq->list, &expired);
++evicted; ++evicted;
} }
spin_unlock(&hb->chain_lock); spin_unlock(&hb->chain_lock);
hlist_for_each_entry_safe(fq, n, &expired, list) hlist_for_each_entry_safe(fq, n, &expired, list_evictor)
f->frag_expire((unsigned long) fq); f->frag_expire((unsigned long) fq);
return evicted; return evicted;
@ -284,8 +283,7 @@ static inline void fq_unlink(struct inet_frag_queue *fq, struct inet_frags *f)
struct inet_frag_bucket *hb; struct inet_frag_bucket *hb;
hb = get_frag_bucket_locked(fq, f); hb = get_frag_bucket_locked(fq, f);
if (!(fq->flags & INET_FRAG_EVICTED)) hlist_del(&fq->list);
hlist_del(&fq->list);
spin_unlock(&hb->chain_lock); spin_unlock(&hb->chain_lock);
} }