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cfq-iosched: fix RCU race in the cfq io_context destructor handling

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put_io_context() drops the RCU read lock before calling into cfq_dtor(),
however we need to hold off freeing there before grabbing and
dereferencing the first object on the list.

So extend the rcu_read_lock() scope to cover the calling of cfq_dtor(),
and optimize cfq_free_io_context() to use a new variant for
call_for_each_cic() that assumes the RCU read lock is already held.

Hit in the wild by Alexey Dobriyan <adobriyan@gmail.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-05-07 09:17:12 +02:00
parent aa94b5371f
commit 07416d29bc
2 changed files with 14 additions and 7 deletions
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2
block/blk-ioc.c
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@ -41,8 +41,8 @@ int put_io_context(struct io_context *ioc)
rcu_read_lock();
if (ioc->aic && ioc->aic->dtor)
ioc->aic->dtor(ioc->aic);
rcu_read_unlock();
cfq_dtor(ioc);
rcu_read_unlock();
kmem_cache_free(iocontext_cachep, ioc);
return 1;