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blackfin: fix possible deadlock in decode_address()

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Oleg Nesterov found an interesting deadlock possibility:

> sysrq_showregs_othercpus() does smp_call_function(showacpu)
> and showacpu() show_stack()->decode_address(). Now suppose that IPI
> interrupts the task holding read_lock(tasklist).

To fix this, blackfin should not grab the write_ variant of the
tasklist lock, read_ one is enough.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Anton Vorontsov 2012-05-31 16:26:24 -07:00 committed by Linus Torvalds
parent 2214f707de
commit af1be5a578
1 changed files with 3 additions and 3 deletions
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6
arch/blackfin/kernel/trace.c
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@ -29,7 +29,7 @@ void decode_address(char *buf, unsigned long address)
{
struct task_struct *p;
struct mm_struct *mm;
unsigned long flags, offset;
unsigned long offset;
struct rb_node *n;
#ifdef CONFIG_KALLSYMS
@ -113,7 +113,7 @@ void decode_address(char *buf, unsigned long address)
* mappings of all our processes and see if we can't be a whee
* bit more specific
*/
write_lock_irqsave(&tasklist_lock, flags);
read_lock(&tasklist_lock);
for_each_process(p) {
struct task_struct *t;
@ -186,7 +186,7 @@ __continue:
sprintf(buf, "/* kernel dynamic memory */");
done:
write_unlock_irqrestore(&tasklist_lock, flags);
read_unlock(&tasklist_lock);
}
#define EXPAND_LEN ((1 << CONFIG_DEBUG_BFIN_HWTRACE_EXPAND_LEN) * 256 - 1)