sched: fix divide by zero at {thread_group,task}_times
On architectures where cputime_t is 64 bit type, is possible to trigger divide by zero on do_div(temp, (__force u32) total) line, if total is a non zero number but has lower 32 bit's zeroed. Removing casting is not a good solution since some do_div() implementations do cast to u32 internally. This problem can be triggered in practice on very long lived processes: PID: 2331 TASK: ffff880472814b00 CPU: 2 COMMAND: "oraagent.bin" #0 [ffff880472a51b70] machine_kexec at ffffffff8103214b #1 [ffff880472a51bd0] crash_kexec at ffffffff810b91c2 #2 [ffff880472a51ca0] oops_end at ffffffff814f0b00 #3 [ffff880472a51cd0] die at ffffffff8100f26b #4 [ffff880472a51d00] do_trap at ffffffff814f03f4 #5 [ffff880472a51d60] do_divide_error at ffffffff8100cfff #6 [ffff880472a51e00] divide_error at ffffffff8100be7b [exception RIP: thread_group_times+0x56] RIP: ffffffff81056a16 RSP: ffff880472a51eb8 RFLAGS: 00010046 RAX: bc3572c9fe12d194 RBX: ffff880874150800 RCX: 0000000110266fad RDX: 0000000000000000 RSI: ffff880472a51eb8 RDI: 001038ae7d9633dc RBP: ffff880472a51ef8 R8: 00000000b10a3a64 R9: ffff880874150800 R10: 00007fcba27ab680 R11: 0000000000000202 R12: ffff880472a51f08 R13: ffff880472a51f10 R14: 0000000000000000 R15: 0000000000000007 ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 #7 [ffff880472a51f00] do_sys_times at ffffffff8108845d #8 [ffff880472a51f40] sys_times at ffffffff81088524 #9 [ffff880472a51f80] system_call_fastpath at ffffffff8100b0f2 RIP: 0000003808caac3a RSP: 00007fcba27ab6d8 RFLAGS: 00000202 RAX: 0000000000000064 RBX: ffffffff8100b0f2 RCX: 0000000000000000 RDX: 00007fcba27ab6e0 RSI: 000000000076d58e RDI: 00007fcba27ab6e0 RBP: 00007fcba27ab700 R8: 0000000000000020 R9: 000000000000091b R10: 00007fcba27ab680 R11: 0000000000000202 R12: 00007fff9ca41940 R13: 0000000000000000 R14: 00007fcba27ac9c0 R15: 00007fff9ca41940 ORIG_RAX: 0000000000000064 CS: 0033 SS: 002b Cc: stable@vger.kernel.org Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/20120808092714.GA3580@redhat.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -3142,6 +3142,20 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
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# define nsecs_to_cputime(__nsecs) nsecs_to_jiffies(__nsecs)
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#endif
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static cputime_t scale_utime(cputime_t utime, cputime_t rtime, cputime_t total)
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{
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u64 temp = (__force u64) rtime;
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temp *= (__force u64) utime;
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if (sizeof(cputime_t) == 4)
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temp = div_u64(temp, (__force u32) total);
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else
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temp = div64_u64(temp, (__force u64) total);
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return (__force cputime_t) temp;
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}
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void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
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{
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cputime_t rtime, utime = p->utime, total = utime + p->stime;
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@ -3151,13 +3165,9 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
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*/
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rtime = nsecs_to_cputime(p->se.sum_exec_runtime);
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if (total) {
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u64 temp = (__force u64) rtime;
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temp *= (__force u64) utime;
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do_div(temp, (__force u32) total);
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utime = (__force cputime_t) temp;
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} else
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if (total)
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utime = scale_utime(utime, rtime, total);
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else
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utime = rtime;
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/*
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@ -3184,13 +3194,9 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
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total = cputime.utime + cputime.stime;
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rtime = nsecs_to_cputime(cputime.sum_exec_runtime);
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if (total) {
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u64 temp = (__force u64) rtime;
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temp *= (__force u64) cputime.utime;
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do_div(temp, (__force u32) total);
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utime = (__force cputime_t) temp;
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} else
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if (total)
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utime = scale_utime(cputime.utime, rtime, total);
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else
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utime = rtime;
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sig->prev_utime = max(sig->prev_utime, utime);
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