# Re: DMA allocations from CMA and fatal\_signal\_pending check

- From: Michal Nazarewicz \<hidden\>
- Date: 2014-11-03 16:45:42 
- List: netdev
- Page: https://ratatoskr.run/netdev/2014/11/4365290
- Thread: https://ratatoskr.run/linux-arm-kernel/2014/10/4361321/t.md

```text
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?

-- 
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.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--[ref]--<xmpp:mina86@jabber.org>--ooO--(_)--Ooo--

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