linux-kernel - RE: [PATCH] dma: zynqmp_dma: Initialize descriptor list after freeing during reset

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Message-ID: <MW2PR02MB37705416E18413689BFFC7C3C9A60@MW2PR02MB3770.namprd02.prod.outlook.com>
Date:   Mon, 4 May 2020 05:33:22 +0000
From:   Harini Katakam <harinik@...inx.com>
To:     Vinod Koul <vkoul@...nel.org>,
        Rafał Hibner <rafal.hibner@...om.com.pl>
CC:     Appana Durga Kedareswara Rao <appanad@...inx.com>,
        Radhey Shyam Pandey <radheys@...inx.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Michal Simek <michals@...inx.com>,
        "open list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM" 
        <dmaengine@...r.kernel.org>,
        "moderated list:ARM/ZYNQ ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] dma: zynqmp_dma: Initialize descriptor list after freeing
 during reset

Hi Vinod,

> -----Original Message-----
> From: Vinod Koul [mailto:vkoul@...nel.org]
> Sent: Monday, May 4, 2020 10:46 AM
> To: Rafał Hibner <rafal.hibner@...om.com.pl>
> Cc: Appana Durga Kedareswara Rao <appanad@...inx.com>; Radhey Shyam
> Pandey <radheys@...inx.com>; Harini Katakam <harinik@...inx.com>; Dan
> Williams <dan.j.williams@...el.com>; Michal Simek <michals@...inx.com>; open
> list:DMA GENERIC OFFLOAD ENGINE SUBSYSTEM
> <dmaengine@...r.kernel.org>; moderated list:ARM/ZYNQ ARCHITECTURE
> <linux-arm-kernel@...ts.infradead.org>; open list <linux-
> kernel@...r.kernel.org>
> Subject: Re: [PATCH] dma: zynqmp_dma: Initialize descriptor list after freeing
> during reset
> 
> On 02-05-20, 15:00, Rafał Hibner wrote:
> > Hello Vinod,
> >
> > On 02.05.2020 14:32, Vinod Koul wrote:
> > > Would it not be better to use list_del_init() where we delete it
> > > rather than do the init here?
> > >
> >
> > It is not a problem of list element itself not being initialized.
> > The problem is that during fault conditions (zynqmp_dma_reset) all
> > elements are moved to free list. List head however is not reinitialized.
> >
> > In normal flow elements are removed by list_del and resubmitted to
> > free list with zynqmp_dma_free_descriptor.
> >
> > static void zynqmp_dma_chan_desc_cleanup(struct zynqmp_dma_chan *chan)
> > {
> >     ...
> >     list_for_each_entry_safe(desc, next, &chan->done_list, node) {
> >         ...
> >         list_del(&desc->node);
> >         ...
> >         zynqmp_dma_free_descriptor(chan, desc);
> >     }
> > }
> >
> > The zynqmp_dma_free_descriptor does not delete elements from the list
> > by itself.
> > I am not he author of this driver so I fixed it by doing non intrusive
> > changes.
> >
> > Anyways, I do not see how using list_del_init would fix the bug.
> 
> Looking at this, i think it would make sense to do list_splice_init() before we
> send the list to be freed.
> 
> Radhey/Appana are cced, they should test this.

I tested this patch (I took over from Appana Kedar).
Once this discussion concludes and Rafal sends a v2, I'll test again and add my tag.

Regards,
Harini