Re: [PATCH 1/1] block: CFQ refcounting fix

[Jens Axboe]

On Wed, Aug 31 2005, Brian King wrote:
> Jens Axboe wrote:
> > On Tue, Aug 30 2005, brking@xxxxxxxxxx wrote:
> > 
> >>I ran across a memory leak related to the cfq scheduler. The cfq
> >>init function increments the refcnt of the associated request_queue.
> >>This refcount gets decremented in cfq's exit function. Since blk_cleanup_queue
> >>only calls the elevator exit function when its refcnt goes to zero, the
> >>request_q never gets cleaned up. It didn't look like other io schedulers were
> >>incrementing this refcnt, so I removed the refcnt increment and it fixed the
> >>memory leak for me.
> >>
> >>To reproduce the problem, simply use cfq and use the scsi_host scan sysfs
> >>attribute to scan "- - -" repeatedly on a scsi host and watch the memory
> >>vanish.
> > 
> > 
> > Yeah, that actually looks like a dangling reference. I assume you tested
> > this properly?
> 
> Yes. I applied the patch, booted my system (which was crashing on
> bootup before due to out of memory errors due to the leak) ran the
> scan a few times and verified /proc/meminfo didn't continually
> decrease like without it, and rebooted again.  If there is anything
> else you would like me to do, I would be happy to do so.

I think you need to remove the blk_put_queue() in cfq_put_cfqd() as
well, otherwise I don't see how this can work without looking at freed
memory. I'll audit the other paths as well.

-- 
Jens Axboe

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