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

From: Jens Axboe
Date: Mon Feb 09 2015 - 12:23:05 EST

On 02/09/2015 06:42 AM, 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.

Thanks, added and marked for stable as well.

Jens Axboe

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