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block: prevent possible io_context->refcount overflow

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Currently io_context has an atomic_t(32-bit) as refcount.  In the case of
cfq, for each device against whcih 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 atomic_long_t.

Signed-off-by: Nikanth Karthikesan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Nikanth Karthikesan 2009-06-10 12:57:06 -07:00 • committed by Jens Axboe
commit d9c7d394a8
3 changed files with 10 additions and 10 deletions
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12
block/blk-ioc.c
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@ -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(atomic_long_read(&ioc->refcount) == 0);
if (atomic_dec_and_test(&ioc->refcount)) {
if (atomic_long_dec_and_test(&ioc->refcount)) {
rcu_read_lock();
if (ioc->aic && ioc->aic->dtor)
ioc->aic->dtor(ioc->aic);
@ -90,7 +90,7 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
ret = kmem_cache_alloc_node(iocontext_cachep, gfp_flags, node);
if (ret) {
atomic_set(&ret->refcount, 1);
atomic_long_set(&ret->refcount, 1);
atomic_set(&ret->nr_tasks, 1);
spin_lock_init(&ret->lock);
ret->ioprio_changed = 0;
@ -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 (!atomic_long_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(atomic_long_read(&src->refcount) == 0);
atomic_long_inc(&src->refcount);
put_io_context(dst);
*pdst = src;
}