From: Robin Murphy <robin.murphy@arm.com>
To: Jason Gunthorpe <jgg@ziepe.ca>,
Christian Benvenuti <benve@cisco.com>,
Nelson Escobar <neescoba@cisco.com>
Cc: linux-rdma@vger.kernel.org, iommu@lists.linux-foundation.org,
umalhi@cisco.com, Dan Carpenter <dan.carpenter@oracle.com>
Subject: Re: [bug report] IB/usnic: Add Cisco VIC low-level hardware driver
Date: Mon, 5 Jul 2021 16:39:16 +0100 [thread overview]
Message-ID: <b2fd45e1-58ee-a695-5560-dc71eca91eb7@arm.com> (raw)
In-Reply-To: <20210705152138.GH4604@ziepe.ca>
On 2021-07-05 16:21, Jason Gunthorpe wrote:
> On Mon, Jul 05, 2021 at 02:47:36PM +0100, Robin Murphy wrote:
>> On 2021-07-05 11:23, Dan Carpenter wrote:
>>> [ Ancient code, but the bug seems real enough still. -dan ]
>>>
>>> Hello Upinder Malhi,
>>>
>>> The patch e3cf00d0a87f: "IB/usnic: Add Cisco VIC low-level hardware
>>> driver" from Sep 10, 2013, leads to the following static checker
>>> warning:
>>>
>>> drivers/iommu/iommu.c:2482 iommu_map()
>>> warn: sleeping in atomic context
>>>
>>> drivers/infiniband/hw/usnic/usnic_uiom.c
>>> 244 static int usnic_uiom_map_sorted_intervals(struct list_head *intervals,
>>> 245 struct usnic_uiom_reg *uiomr)
>>>
>>> This function is always called from usnic_uiom_reg_get() which is holding
>>> spin_lock(&pd->lock); so it can't sleep.
>>
>> FWIW back in those days it wasn't really well defined whether iommu_map()
>> was callable from non-sleeping contexts (the arch/arm DMA API code relied on
>> it, for instance). It was only formalised 2 years ago by 781ca2de89ba
>> ("iommu: Add gfp parameter to iommu_ops::map") which introduced the
>> might_sleep() check that's firing there. I guess these calls want to be
>> updated to iommu_map_atomic() now.
>
> Does this mean this driver doesn't work at all upstream? I would be
> quite interested to delete it.
I think the only time it's actually in trouble is on AMD hardware if one
of those iommu_map() calls has to allocate a new pagetable page and that
allocation has to go down whichever reclaim path actually sleeps.
Historically all the other IOMMU drivers it might have come into contact
with already used GFP_ATOMIC for their internal allocations anyway (AMD
was the only one using a mutex instead of a spinlock internally), and
some like intel-iommu still haven't relaxed that even now.
Robin.
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next prev parent reply other threads:[~2021-07-05 15:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-05 10:23 [bug report] IB/usnic: Add Cisco VIC low-level hardware driver Dan Carpenter
2021-07-05 13:47 ` Robin Murphy
2021-07-05 15:21 ` Jason Gunthorpe
2021-07-05 15:39 ` Robin Murphy [this message]
2021-07-05 15:45 ` Dan Carpenter
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