/proc/*/oom_score oops re badness
Alexey Dobriyan [Tue, 8 May 2007 07:26:46 +0000 (00:26 -0700)]
Eternal quest to make

while true; do cat /proc/fs/xfs/stat >/dev/null 2>/dev/null; done
while true; do find /proc -type f 2>/dev/null | xargs cat >/dev/null 2>/dev/null; done
while true; do modprobe xfs; rmmod xfs; done

work reliably continues and now kernel oopses in the following way:

BUG: unable to handle ... at virtual address 6b6b6b6b
EIP is at badness
process: cat
proc_oom_score
proc_info_read
sys_fstat64
vfs_read
proc_info_read
sys_read

Failing code is prefetch hidden in list_for_each_entry() in badness().
badness() is reachable from two points. One is proc_oom_score, another
is out_of_memory() => select_bad_process() => badness().

Second path grabs tasklist_lock, while first doesn't.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

index 0697fd0..ab1b439 100644 (file)
@@ -314,7 +314,9 @@ static int proc_oom_score(struct task_struct *task, char *buffer)
        struct timespec uptime;
 
        do_posix_clock_monotonic_gettime(&uptime);
+       read_lock(&tasklist_lock);
        points = badness(task, uptime.tv_sec);
+       read_unlock(&tasklist_lock);
        return sprintf(buffer, "%lu\n", points);
 }