linux-kernel - Re: [PATCH v2] dmaengine: idxd: avoid deadlock in process_misc

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Date:   Tue, 23 Aug 2022 17:54:35 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH v2] dmaengine: idxd: avoid deadlock in
 process_misc_interrupts()

On Tue, Aug 23, 2022 at 09:46:19AM -0700, Dave Jiang wrote:
> 
> On 8/23/2022 9:37 AM, Jerry Snitselaar wrote:
> > idxd_device_clear_state() now grabs the idxd->dev_lock
> > itself, so don't grab the lock prior to calling it.
> > 
> > This was seen in testing after dmar fault occurred on system,
> > resulting in lockup stack traces.
> > 
> > Cc: Fenghua Yu <fenghua.yu@...el.com>
> > Cc: Dave Jiang <dave.jiang@...el.com>
> > Cc: Vinod Koul <vkoul@...nel.org>
> > Cc: dmaengine@...r.kernel.org
> > Fixes: cf4ac3fef338 ("dmaengine: idxd: fix lockdep warning on device driver removal")
> > Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>
> 
> Thanks Jerry!
> 
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> 

I noticed another problem while looking at this. When the device ends
up in the halted state, and needs an flr or system reset, it calls
idxd_wqs_unmap_portal(). Then if you do a modprobe -r idxd, you hit
the WARN_ON in devm_iounmap(), because the remove code path calls
idxd_wq_portal_unmap(), and wq->portal is null. I'm not sure if it
just needs a simple sanity check in drv_disable_wq() to avoid the call
in the case that it has already been unmapped, or if more cleanup
needs to be done, and possibly a state to differentiate between
halted + soft reset possible, versus halted + flr or system reset
needed.  You get multiple "Device is HALTED" messages during the
removal as well.

Regards,
Jerry