linux-kernel - Re: [PATCH] iommu: Properly pass gfp_t in _iommu

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Date:   Tue, 2 Feb 2021 13:52:22 +0000
From:   Will Deacon <will@...nel.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Yong Wu <yong.wu@...iatek.com>, joro@...tes.org,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Properly pass gfp_t in _iommu_map() to avoid
 atomic sleeping

On Mon, Feb 01, 2021 at 05:06:23PM -0800, Douglas Anderson wrote:
> Sleeping while atomic = bad.  Let's fix an obvious typo to try to avoid it.
> 
> The warning that was seen (on a downstream kernel with the problematic
> patch backported):
> 
>  BUG: sleeping function called from invalid context at mm/page_alloc.c:4726
>  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 9, name: ksoftirqd/0
>  CPU: 0 PID: 9 Comm: ksoftirqd/0 Not tainted 5.4.93-12508-gc10c93e28e39 #1
>  Call trace:
>   dump_backtrace+0x0/0x154
>   show_stack+0x20/0x2c
>   dump_stack+0xa0/0xfc
>   ___might_sleep+0x11c/0x12c
>   __might_sleep+0x50/0x84
>   __alloc_pages_nodemask+0xf8/0x2bc
>   __arm_lpae_alloc_pages+0x48/0x1b4
>   __arm_lpae_map+0x124/0x274
>   __arm_lpae_map+0x1cc/0x274
>   arm_lpae_map+0x140/0x170
>   arm_smmu_map+0x78/0xbc

Damn, I'm annoyed that I didn't come across this in testing. Looks like
arm64 defconfig doesn't have DEBUG_ATOMIC_SLEEP, so that's probably why.
I'll see if I can adjust my scripts to enable that (and some others) for
the builds I actually run.

>   __iommu_map+0xd4/0x210
>   _iommu_map+0x4c/0x84
>   iommu_map_atomic+0x44/0x58
>   __iommu_dma_map+0x8c/0xc4
>   iommu_dma_map_page+0xac/0xf0
> 
> Fixes: d8c1df02ac7f ("iommu: Move iotlb_sync_map out from __iommu_map")
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> I haven't done any serious testing on this.  I saw a report of the
> warning and the fix seemed obvious so I'm shooting it out.
> 
>  drivers/iommu/iommu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Acked-by: Will Deacon <will@...nel.org>

Joerg -- please can you apply this one on top of the pull request I sent
yesterday?

Cheers,

Will