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:

quoted

On Fri, Aug 30, 2019 at 09:31:17PM +0800, Jing Xiangfeng wrote:

quoted

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 <redacted>

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.

-- 
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