Commit 2214f707 authored by Anton Vorontsov's avatar Anton Vorontsov Committed by Linus Torvalds
Browse files

blackfin: a couple of task->mm handling fixes 



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: 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 1198c8b9

arch/blackfin/kernel/trace.c

+13 −13
Original line number Diff line number Diff line
@@ -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)

			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;
@@ -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);

	}



	/*

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