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blackfin: a couple of task->mm handling fixes

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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>
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 1198c8b9af
commit 2214f707de
1 changed files with 13 additions and 13 deletions
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26
arch/blackfin/kernel/trace.c
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@ -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>
@ -28,7 +30,6 @@ 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
@ -114,15 +115,15 @@ 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)
struct task_struct *t;
t = find_lock_task_mm(p);
if (!t)
continue;
if (!down_read_trylock(&mm->mmap_sem)) {
if (!in_atomic)
mmput(mm);
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;
@ -131,7 +132,7 @@ 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) {
@ -164,8 +165,7 @@ 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);
@ -175,8 +175,8 @@ void decode_address(char *buf, unsigned long address)
}
up_read(&mm->mmap_sem);
if (!in_atomic)
mmput(mm);
__continue:
task_unlock(t);
}
/*