Messages in this thread Patch in this message | | | From | Nikanth Karthikesan <> | Subject | [PATCH][RFC] Handle improbable possibility of io_context->refcount overflow | Date | Wed, 29 Apr 2009 12:21:39 +0530 |
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Hi Jens
Currently io_context has an atomic_t(int) as refcount. In case of cfq, for each device a task does I/O, a reference to the io_context would be taken. And when there are multiple process sharing io_contexts(CLONE_IO) would also have a reference to the same io_context. Theoretically the possible maximum number of processes sharing the same io_context + the number of disks/cfq_data referring to the same io_context can overflow the 32-bit counter on a very high-end machine. Even though it is an improbable case, let us make it difficult by changing the refcount to atomic64_t(long).
Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
---
diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 012f065..4f5ff79 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -35,9 +35,9 @@ int put_io_context(struct io_context *ioc) if (ioc == NULL) return 1; - BUG_ON(atomic_read(&ioc->refcount) == 0); + BUG_ON(atomic64_read(&ioc->refcount) == 0); - if (atomic_dec_and_test(&ioc->refcount)) { + if (atomic64_dec_and_test(&ioc->refcount)) { rcu_read_lock(); if (ioc->aic && ioc->aic->dtor) ioc->aic->dtor(ioc->aic); @@ -151,7 +151,7 @@ struct io_context *get_io_context(gfp_t gfp_flags, int node) ret = current_io_context(gfp_flags, node); if (unlikely(!ret)) break; - } while (!atomic_inc_not_zero(&ret->refcount)); + } while (!atomic64_inc_not_zero(&ret->refcount)); return ret; } @@ -163,8 +163,8 @@ void copy_io_context(struct io_context **pdst, struct io_context **psrc) struct io_context *dst = *pdst; if (src) { - BUG_ON(atomic_read(&src->refcount) == 0); - atomic_inc(&src->refcount); + BUG_ON(atomic64_read(&src->refcount) == 0); + atomic64_inc(&src->refcount); put_io_context(dst); *pdst = src; } diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index a55a9bd..f829bd2 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1282,7 +1282,7 @@ static void cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq) if (!cfqd->active_cic) { struct cfq_io_context *cic = RQ_CIC(rq); - atomic_inc(&cic->ioc->refcount); + atomic64_inc(&cic->ioc->refcount); cfqd->active_cic = cic; } } diff --git a/include/linux/iocontext.h b/include/linux/iocontext.h index 08b987b..f1a57f4 100644 --- a/include/linux/iocontext.h +++ b/include/linux/iocontext.h @@ -64,7 +64,7 @@ struct cfq_io_context { * and kmalloc'ed. These could be shared between processes. */ struct io_context { - atomic_t refcount; + atomic64_t refcount; atomic_t nr_tasks; /* all the fields below are protected by this lock */ @@ -91,7 +91,7 @@ static inline struct io_context *ioc_task_link(struct io_context *ioc) * if ref count is zero, don't allow sharing (ioc is going away, it's * a race). */ - if (ioc && atomic_inc_not_zero(&ioc->refcount)) { + if (ioc && atomic64_inc_not_zero(&ioc->refcount)) { atomic_inc(&ioc->nr_tasks); return ioc; }
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