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Date:   Mon, 10 Oct 2022 11:57:39 -0700
From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Christoph Hellwig <hch@lst.de>, Robin Murphy <robin.murphy@arm.com>
Cc:     Joerg Roedel <joro@8bytes.org>, iommu@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Issue seen since commit f5ff79fddf0e ("dma-mapping: remove
 CONFIG_DMA_REMAP")
Message-ID: <20221010185739.vgw27m7fpmftly3q@cantor>
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I've been looking at an odd issue that shows up with commit
f5ff79fddf0e ("dma-mapping: remove CONFIG_DMA_REMAP").  What is being
seen is the bnx2fc driver calling dma_free_coherent(), and eventually
hits the BUG_ON() in vunmap().  bnx2fc_free_session_resc() does a
spin_lock_bh() around the dma_free_coherent() calls, and looking at
preempt.h that will trigger in_interrupt() to return positive, so that
makes sense. The really odd part is this only happens with the
shutdown of the kernel after a system install. Reboots after that do not
hit the BUG_ON() in vunmap().

I still need to grab a system and try to see what it is doing on the
subsequent shutdowns, because it seems to me that any time
bnx2fc_free_session_resc() is called it will end up there, unless the
allocs are not coming from vmalloc() in the later boots. Between the
comments in dma_free_attrs(), and preempt.h, dma_free_coherent()
shouldn't be called under a spin_lock_bh(), yes? I think the comments
in dma_free_attrs() might be out of date with commit f5ff79fddf0e
("dma-mapping: remove CONFIG_DMA_REMAP") in place since now it is more
general that you can land in vunmap(). Also, should that WARN_ON() in
dma_free_attrs() trigger as well for the BH disabled case?

It was also reproduced with a 6.0-rc5 kernel build[1].

Regards,
Jerry


[1] https://koji.fedoraproject.org/koji/buildinfo?buildID=2061881