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nios2: time: Read timer in get_cycles only if initialized
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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: 33d72f3 ("init/main.c: extract early boot entropy from the ..")
Cc: Laura Abbott <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Daniel Micay <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
groeck authored and Ley Foon Tan committed Sep 15, 2017
1 parent 8993d5e commit 65d1e3d
Showing 1 changed file with 4 additions and 1 deletion.
5 changes: 4 additions & 1 deletion arch/nios2/kernel/time.c
Original file line number Diff line number Diff line change
@@ -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);

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