diff options
| author | Stanislaw Gruszka <sgruszka@redhat.com> | 2012-08-08 11:27:15 +0200 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2012-09-12 03:36:59 +0100 |
| commit | 097e2f40cbca70422ade38ea61d72c3b8566f14d (patch) | |
| tree | 235b890600213c6e619f5bf6899842f3ec9de88c /kernel/sched.c | |
| parent | 7599224c6ce9a07a5343ed37b6da3aef3ceab5ee (diff) | |
sched: fix divide by zero at {thread_group,task}_times
commit bea6832cc8c4a0a9a65dd17da6aaa657fe27bc3e upstream.
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
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>
[bwh: Backported to 3.2:
- Adjust filename
- Most conversions in the original code are implicit]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'kernel/sched.c')
| -rw-r--r-- | kernel/sched.c | 34 |
1 files changed, 20 insertions, 14 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index e0431c4f11f9..910db7d543cc 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -4355,6 +4355,20 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st) # define nsecs_to_cputime(__nsecs) nsecs_to_jiffies(__nsecs) #endif +static cputime_t scale_utime(cputime_t utime, cputime_t rtime, cputime_t total) +{ + u64 temp = (__force u64) rtime; + + temp *= (__force u64) utime; + + if (sizeof(cputime_t) == 4) + temp = div_u64(temp, (__force u32) total); + else + temp = div64_u64(temp, (__force u64) total); + + return (__force cputime_t) temp; +} + void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st) { cputime_t rtime, utime = p->utime, total = cputime_add(utime, p->stime); @@ -4364,13 +4378,9 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st) */ rtime = nsecs_to_cputime(p->se.sum_exec_runtime); - if (total) { - u64 temp = rtime; - - temp *= utime; - do_div(temp, total); - utime = (cputime_t)temp; - } else + if (total) + utime = scale_utime(utime, rtime, total); + else utime = rtime; /* @@ -4397,13 +4407,9 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st) total = cputime_add(cputime.utime, cputime.stime); rtime = nsecs_to_cputime(cputime.sum_exec_runtime); - if (total) { - u64 temp = rtime; - - temp *= cputime.utime; - do_div(temp, total); - utime = (cputime_t)temp; - } else + if (total) + utime = scale_utime(cputime.utime, rtime, total); + else utime = rtime; sig->prev_utime = max(sig->prev_utime, utime); |