From: mina86@mina86•com (Michal Nazarewicz)
To: linux-arm-kernel@lists•infradead.org
Subject: DMA allocations from CMA and fatal_signal_pending check
Date: Mon, 03 Nov 2014 17:45:31 +0100 [thread overview]
Message-ID: <xa1tlhnsw7v8.fsf@mina86.com> (raw)
In-Reply-To: <5453F80C.4090006@gmail.com>
On Fri, Oct 31 2014, Florian Fainelli wrote:
> I agree that the CMA allocation should not be allowed to succeed, but
> the dma_alloc_coherent() allocation should succeed. If we look at the
> sysport driver, there are kmalloc() calls to initialize private
> structures, those will succeed (except under high memory pressure), so
> by the same token, a driver expects DMA allocations to succeed (unless
> we are under high memory pressure)
>
> What are we trying to solve exactly with the fatal_signal_pending()
> check here? Are we just optimizing for the case where a process has
> allocated from a CMA region to allow this region to be returned to the
> pool of free pages when it gets killed? Could there be another mechanism
> used to reclaim those pages if we know the process is getting killed
> anyway?
We're guarding against situations where process may hang around
arbitrarily long time after receiving SIGKILL. If user does ?kill -9
$pid? the usual expectation is that the $pid process will die within
seconds and anything longer is perceived by user as a bug.
What problem are *you* trying to solve? If user sent SIGKILL to
a process that imitated device initialisation, what is the point of
continuing initialising the device? Just recover and return -EINTR.
> Well, not really. This driver is not an isolated case, there are tons of
> other networking drivers that do exactly the same thing, and we do
> expect these dma_alloc_* calls to succeed.
Again, why do you expect them to succeed? The code must handle failures
correctly anyway so why do you wish to ignore fatal signal?
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Micha? ?mina86? Nazarewicz (o o)
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next prev parent reply other threads:[~2014-11-03 16:45 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-28 19:08 DMA allocations from CMA and fatal_signal_pending check Florian Fainelli
2014-10-31 8:28 ` Joonsoo Kim
2014-10-31 20:58 ` Florian Fainelli
2014-11-03 16:45 ` Michal Nazarewicz [this message]
2014-11-03 18:51 ` Florian Fainelli
2014-10-31 21:07 ` Maxime Bizon
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