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 44bbf2f..d08f0e3 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> @@ -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); }
/*