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nios2: time: Read timer in get_cycles only if initialized 

Mainline crashes as follows when running nios2 images.

On node 0 totalpages: 65536
free_area_init_node: node 0, pgdat c8408fa0, node_mem_map c8726000
  Normal zone: 512 pages used for memmap
  Normal zone: 0 pages reserved
  Normal zone: 65536 pages, LIFO batch:15
Unable to handle kernel NULL pointer dereference at virtual address 00000000
ea = c8003cb0, ra = c81cbf40, cause = 15
Kernel panic - not syncing: Oops

Problem is seen because get_cycles() is called before the timer it depends
on is initialized. Returning 0 in that situation fixes the problem.

Fixes: 33d72f3822 ("init/main.c: extract early boot entropy from the ..")
Cc: Laura Abbott <labbott@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
This commit is contained in:
Guenter Roeck 2017-09-11 20:45:26 -07:00 committed by Ley Foon Tan
parent 8993d5e466
commit 65d1e3ddea
1 changed files with 4 additions and 1 deletions
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5
arch/nios2/kernel/time.c
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@ -107,7 +107,10 @@ static struct nios2_clocksource nios2_cs = {
cycles_t get_cycles(void)
{
return nios2_timer_read(&nios2_cs.cs);
/* Only read timer if it has been initialized */
if (nios2_cs.timer.base)
return nios2_timer_read(&nios2_cs.cs);
return 0;
}
EXPORT_SYMBOL(get_cycles);