Re: [PATCH] iommu: Properly pass gfp_t in _iommu_map() to avoid atomic sleeping

Will Deacon
2021-02-02T17:36:54Z

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@chromium.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@kernel.org>

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

Cheers,

Will