kmemleak: Fix scheduling-while-atomic bug
One of the kmemleak changes caused the following
scheduling-while-holding-the-tasklist-lock regression on x86:
BUG: sleeping function called from invalid context at mm/kmemleak.c:795
in_atomic(): 1, irqs_disabled(): 0, pid: 1737, name: kmemleak
2 locks held by kmemleak/1737:
#0: (scan_mutex){......}, at: [<c10c4376>] kmemleak_scan_thread+0x45/0x86
#1: (tasklist_lock){......}, at: [<c10c3bb4>] kmemleak_scan+0x1a9/0x39c
Pid: 1737, comm: kmemleak Not tainted 2.6.31-rc1-tip #59266
Call Trace:
[<c105ac0f>] ? __debug_show_held_locks+0x1e/0x20
[<c102e490>] __might_sleep+0x10a/0x111
[<c10c38d5>] scan_yield+0x17/0x3b
[<c10c3970>] scan_block+0x39/0xd4
[<c10c3bc6>] kmemleak_scan+0x1bb/0x39c
[<c10c4331>] ? kmemleak_scan_thread+0x0/0x86
[<c10c437b>] kmemleak_scan_thread+0x4a/0x86
[<c104d73e>] kthread+0x6e/0x73
[<c104d6d0>] ? kthread+0x0/0x73
[<c100959f>] kernel_thread_helper+0x7/0x10
kmemleak: 834 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
The bit causing it is highly dubious:
static void scan_yield(void)
{
might_sleep();
if (time_is_before_eq_jiffies(next_scan_yield)) {
schedule();
next_scan_yield = jiffies + jiffies_scan_yield;
}
}
It called deep inside the codepath and in a conditional way,
and that is what crapped up when one of the new scan_block()
uses grew a tasklist_lock dependency.
This minimal patch removes that yielding stuff and adds the
proper cond_resched().
The background scanning thread could probably also be reniced
to +10.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index eeece2d..e766e1d 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -105,7 +105,6 @@
#define MAX_TRACE 16 /* stack trace length */
#define REPORTS_NR 50 /* maximum number of reported leaks */
#define MSECS_MIN_AGE 5000 /* minimum object age for reporting */
-#define MSECS_SCAN_YIELD 10 /* CPU yielding period */
#define SECS_FIRST_SCAN 60 /* delay before the first scan */
#define SECS_SCAN_WAIT 600 /* subsequent auto scanning delay */
@@ -186,10 +185,7 @@
static unsigned long min_addr = ULONG_MAX;
static unsigned long max_addr;
-/* used for yielding the CPU to other tasks during scanning */
-static unsigned long next_scan_yield;
static struct task_struct *scan_thread;
-static unsigned long jiffies_scan_yield;
/* used to avoid reporting of recently allocated objects */
static unsigned long jiffies_min_age;
static unsigned long jiffies_last_scan;
@@ -786,21 +782,6 @@
EXPORT_SYMBOL(kmemleak_no_scan);
/*
- * Yield the CPU so that other tasks get a chance to run. The yielding is
- * rate-limited to avoid excessive number of calls to the schedule() function
- * during memory scanning.
- */
-static void scan_yield(void)
-{
- might_sleep();
-
- if (time_is_before_eq_jiffies(next_scan_yield)) {
- schedule();
- next_scan_yield = jiffies + jiffies_scan_yield;
- }
-}
-
-/*
* Memory scanning is a long process and it needs to be interruptable. This
* function checks whether such interrupt condition occured.
*/
@@ -840,15 +821,6 @@
if (scan_should_stop())
break;
- /*
- * When scanning a memory block with a corresponding
- * kmemleak_object, the CPU yielding is handled in the calling
- * code since it holds the object->lock to avoid the block
- * freeing.
- */
- if (!scanned)
- scan_yield();
-
object = find_and_get_object(pointer, 1);
if (!object)
continue;
@@ -1014,7 +986,7 @@
*/
object = list_entry(gray_list.next, typeof(*object), gray_list);
while (&object->gray_list != &gray_list) {
- scan_yield();
+ cond_resched();
/* may add new objects to the list */
if (!scan_should_stop())
@@ -1385,7 +1357,6 @@
int i;
unsigned long flags;
- jiffies_scan_yield = msecs_to_jiffies(MSECS_SCAN_YIELD);
jiffies_min_age = msecs_to_jiffies(MSECS_MIN_AGE);
jiffies_scan_wait = msecs_to_jiffies(SECS_SCAN_WAIT * 1000);