From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Jing Xiangfeng <jingxiangfeng@huawei.com>
Cc: ebiederm@xmission.com, kstewart@linuxfoundation.org,
gregkh@linuxfoundation.org, gustavo@embeddedor.com,
bhelgaas@google.com, tglx@linutronix.de,
sakari.ailus@linux.intel.com,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] arm: fix page faults in do_alignment
Date: Sat, 31 Aug 2019 08:55:24 +0100 [thread overview]
Message-ID: <20190831075524.GI13294@shell.armlinux.org.uk> (raw)
In-Reply-To: <5D69D239.2080908@huawei.com>
On Sat, Aug 31, 2019 at 09:49:45AM +0800, Jing Xiangfeng wrote:
> On 2019/8/30 21:35, Russell King - ARM Linux admin wrote:
> > On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote:
> >> The function do_alignment can handle misaligned address for user and
> >> kernel space. If it is a userspace access, do_alignment may fail on
> >> a low-memory situation, because page faults are disabled in
> >> probe_kernel_address.
> >>
> >> Fix this by using __copy_from_user stead of probe_kernel_address.
> >>
> >> Fixes: b255188 ("ARM: fix scheduling while atomic warning in alignment handling code")
> >> Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
> >
> > NAK.
> >
> > The "scheduling while atomic warning in alignment handling code" is
> > caused by fixing up the page fault while trying to handle the
> > mis-alignment fault generated from an instruction in atomic context.
>
> __might_sleep is called in the function __get_user which lead to that bug.
> And that bug is triggered in a kernel space. Page fault can not be generated.
> Right?
Your email is now fixed?
All of get_user(), __get_user(), copy_from_user() and __copy_from_user()
_can_ cause a page fault, which might need to fetch the page from disk.
All these four functions are equivalent as far as that goes - and indeed
as are their versions that write as well.
If the page needs to come from disk, all of these functions _will_
sleep. If they are called from an atomic context, and the page fault
handler needs to fetch data from disk, they will attempt to sleep,
which will issue a warning.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up
next prev parent reply other threads:[~2019-08-31 8:01 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 13:31 [PATCH] arm: fix page faults in do_alignment Jing Xiangfeng
2019-08-30 13:35 ` Russell King - ARM Linux admin
2019-08-30 13:48 ` Russell King - ARM Linux admin
2019-08-30 19:45 ` Eric W. Biederman
2019-08-30 20:30 ` Russell King - ARM Linux admin
2019-08-30 21:02 ` Eric W. Biederman
2019-08-30 22:29 ` Russell King - ARM Linux admin
2019-09-02 17:36 ` Eric W. Biederman
2019-09-04 2:17 ` Jing Xiangfeng
2019-09-06 15:17 ` Russell King - ARM Linux admin
2019-09-15 18:34 ` Russell King - ARM Linux admin
2019-09-16 14:31 ` Eric W. Biederman
2019-08-31 1:49 ` Jing Xiangfeng
2019-08-31 7:55 ` Russell King - ARM Linux admin [this message]
2019-08-31 9:16 ` Jing Xiangfeng
2019-08-31 12:48 ` kbuild test robot
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