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Subject[PATCH 6/9] 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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
arch/blackfin/kernel/trace.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/blackfin/kernel/trace.c b/arch/blackfin/kernel/trace.c
index d08f0e3..f7f7a18 100644
--- a/arch/blackfin/kernel/trace.c
+++ b/arch/blackfin/kernel/trace.c
@@ -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)
--
1.7.9.2


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