Re: [PATCH v2] blkmq: Fix NULL pointer deref when all reserved tags in use

[Jens Axboe]

On 03/18/2015 05:07 PM, Sam Bradshaw wrote:
> When allocating from the reserved tags pool, bt_get() is called with
> a NULL hctx.  If all tags are in use, the hw queue is kicked to push
> out any pending IO, potentially freeing tags, and tag allocation is
> retried.  The problem is that blk_mq_run_hw_queue() doesn't check for
> a NULL hctx.  So we avoid it with a simple NULL hctx test.
>
> This issue was introduced by:
> b32232073e80: blk-mq: fix hang in bt_get()
>
> Tested by hammering mtip32xx with concurrent smartctl/hdparm.
>
> Signed-off-by: Sam Bradshaw <sbradshaw@xxxxxxxxxx>
> Signed-off-by: Selvan Mani <smani@xxxxxxxxxx>

Thanks Sam, added to the current series.

--
Jens Axboe

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