From mboxrd@z Thu Jan  1 00:00:00 1970
From: ming.lei@redhat.com (Ming Lei)
Date: Tue, 12 Dec 2017 17:16:59 +0800
Subject: BUG: NULL pointer at IP: blk_mq_map_swqueue+0xbc/0x200 on
 4.15.0-rc2
In-Reply-To: <20171212083502.GA10646@infradead.org>
References: <799322399.34367785.1512659684033.JavaMail.zimbra@redhat.com>
 <1443577037.35143768.1512717869183.JavaMail.zimbra@redhat.com>
 <20171211035844.GB22819@ming.t460p>
 <20171212083502.GA10646@infradead.org>
Message-ID: <20171212091658.GA8529@ming.t460p>

On Tue, Dec 12, 2017@12:35:02AM -0800, Christoph Hellwig wrote:
> On Mon, Dec 11, 2017@11:58:45AM +0800, Ming Lei wrote:
> > As we talked offline, this IP points to cpumask_set_cpu(), seems this
> > case may happen when one CPU isn't mapped to any hw queue, could you test
> > the following patch to see if it helps your issue?
> 
> This looks odd as mq_map should be pre-zeroed.  If it isn't we have
> a few more problems..

This happens in case of updating nr_hw_queue, for example, when the
number becomes 5 from 12, then the table has to be zeroed for avoiding
obsolete mapping if one CPU isn't mapped to any hw queue.

Thanks,
Ming