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Commit af1be5a5 authored by Anton Vorontsov's avatar Anton Vorontsov Committed by Linus Torvalds
Browse files

blackfin: fix possible deadlock in decode_address() 



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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarAnton Vorontsov <anton.vorontsov@linaro.org>
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2214f707

arch/blackfin/kernel/trace.c

+3 −3
Original line number Diff line number Diff line
@@ -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 @@ void decode_address(char *buf, unsigned long address) 
	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)