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Date: Mon, 11 Sep 2017 20:45:26 -0700 From: Guenter Roeck <linux@...ck-us.net> To: Ley Foon Tan <lftan@...era.com> Cc: nios2-dev@...ts.rocketboards.org, linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>, Laura Abbott <labbott@...hat.com>, Kees Cook <keescook@...omium.org>, Daniel Micay <danielmicay@...il.com> Subject: [PATCH] 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: 33d72f3822d7 ("init/main.c: extract early boot entropy from the ..") Cc: Laura Abbott <labbott@...hat.com> Cc: Kees Cook <keescook@...omium.org> Cc: Daniel Micay <danielmicay@...il.com> Signed-off-by: Guenter Roeck <linux@...ck-us.net> --- Taking a stab at the problem. Fix works for my qemu test. arch/nios2/kernel/time.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/nios2/kernel/time.c b/arch/nios2/kernel/time.c index 645129aaa9a0..20e86209ef2e 100644 --- a/arch/nios2/kernel/time.c +++ b/arch/nios2/kernel/time.c @@ -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); -- 2.7.4
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