Commit 1f8a7633 authored Dec 05, 2014 by Tetsuo Handa Committed by Ingo Molnar Jan 14, 2015

sched/debug: Fix potential call to __ffs(0) in sched_show_task()



"struct task_struct"->state is "volatile long" and __ffs() warns that
"Undefined if no bit exists, so code should check against 0 first."

Therefore, at expression

  state = p->state ? __ffs(p->state) + 1 : 0;

in sched_show_task(), CPU might see "p->state" before "?" as "non-zero"
but "p->state" after "?" as "zero", which could result in
"state >= sizeof(stat_nam)" being true and bogus '?' is printed.

This patch changes "state" from "unsigned int" to "unsigned long" and
save "p->state" before calling __ffs(), in order to avoid potential call
to __ffs(0).

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/201412052131.GCE35924.FVHFOtLOJOMQFS@I-love.SAKURA.ne.jp


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent a8b686b3

kernel/sched/core.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -4508,9 +4508,10 @@ void sched_show_task(struct task_struct *p)
		{
		unsigned long free = 0;
		int ppid;
		unsigned state;
		unsigned long state = p->state;

		state = p->state ? __ffs(p->state) + 1 : 0;
		if (state)
		state = __ffs(state) + 1;
		printk(KERN_INFO "%-15.15s %c", p->comm,
		state < sizeof(stat_nam) - 1 ? stat_nam[state] : '?');
		#if BITS_PER_LONG == 32

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