Re: [PATCH] cfq-iosched: handle failure of cfq group allocation

From: Tejun Heo
Date: Mon Feb 09 2015 - 08:45:46 EST

On Mon, Feb 09, 2015 at 04:42:49PM +0300, Konstantin Khlebnikov wrote:
> Cfq_lookup_create_cfqg() allocates struct blkcg_gq using GFP_ATOMIC.
> In cfq_find_alloc_queue() possible allocation failure is not handled.
> As a result kernel oopses on NULL pointer dereference when
> cfq_link_cfqq_cfqg() calls cfqg_get() for NULL pointer.
> Bug was introduced in v3.5 in commit cd1604fab4f9 ("blkcg: factor
> out blkio_group creation"). Prior to that commit cfq group lookup
> had returned pointer to root group as fallback.
> This patch handles this error using existing fallback oom_cfqq.
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>


Acked-by: Tejun Heo <tj@xxxxxxxxxx>


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