[PATCH 05/10] blackfin: A couple of task->mm handling fixes

Anton Vorontsov
2012-03-24T10:30:56Z

The patch fixes two problems:

1. Working with task->mm w/o getting mm or grabing the task lock is
dangerous as ->mm might disappear (exit_mm() assigns NULL under
task_lock(), so tasklist lock is not enough).

We can't use get_task_mm()/mmput() pair as mmput() might sleep,
so we have to take the task lock while handle its mm.

2. Checking for process->mm is not enough because process' main
thread may exit or detach its mm via use_mm(), but other threads
may still have a valid mm.

To catch this we use find_lock_task_mm(), which walks up all
threads and returns an appropriate task (with task lock held).

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
arch/blackfin/kernel/trace.c | 26 +++++++++++++-------------
1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/blackfin/kernel/trace.c b/arch/blackfin/kernel/trace.c
index 050db44..5102cdf 100644
--- a/arch/blackfin/kernel/trace.c
+++ b/arch/blackfin/kernel/trace.c
@@ -10,6 +10,8 @@
#include <linux/hardirq.h>
#include <linux/thread_info.h>
#include <linux/mm.h>
+#include <linux/oom.h>
+#include <linux/sched.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
@@ -27,7 +29,6 @@ void decode_address(char *buf, unsigned long address)
struct task_struct *p;
struct mm_struct *mm;
unsigned long flags, offset;
- unsigned char in_atomic = (bfin_read_IPEND() & 0x10) || in_atomic();
struct rb_node *n;

#ifdef CONFIG_KALLSYMS
@@ -113,15 +114,15 @@ void decode_address(char *buf, unsigned long address)
*/
write_lock_irqsave(&tasklist_lock, flags);
for_each_process(p) {
- mm = (in_atomic ? p->mm : get_task_mm(p));
- if (!mm)
- continue;
+ struct task_struct *t;

- if (!down_read_trylock(&mm->mmap_sem)) {
- if (!in_atomic)
- mmput(mm);
+ t = find_lock_task_mm(p);
+ if (!t)
continue;
- }
+
+ mm = t->mm;
+ if (!down_read_trylock(&mm->mmap_sem))
+ goto __continue;

for (n = rb_first(&mm->mm_rb); n; n = rb_next(n)) {
struct vm_area_struct *vma;
@@ -130,7 +131,7 @@ void decode_address(char *buf, unsigned long address)

if (address >= vma->vm_start && address < vma->vm_end) {
char _tmpbuf[256];
- char *name = p->comm;
+ char *name = t->comm;
struct file *file = vma->vm_file;

if (file) {
@@ -163,8 +164,7 @@ void decode_address(char *buf, unsigned long address)
name, vma->vm_start, vma->vm_end);

up_read(&mm->mmap_sem);
- if (!in_atomic)
- mmput(mm);
+ task_unlock(t);

if (buf[0] == '\0')
sprintf(buf, "[ %s ] dynamic memory", name);
@@ -174,8 +174,8 @@ void decode_address(char *buf, unsigned long address)
}

up_read(&mm->mmap_sem);
- if (!in_atomic)
- mmput(mm);
+__continue:
+ task_unlock(t);
}

/*
--
1.7.9.2