The patch titled
Subject: kfence: fix potential deadlock due to wake_up()
has been added to the -mm tree. Its filename is
mm-add-kernel-electric-fence-infrastructure-fix-3.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-add-kernel-electric-fence-infrastructure-fix-3.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-add-kernel-electric-fence-infrastructure-fix-3.patch
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------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: kfence: fix potential deadlock due to wake_up()
Lockdep reports that we may deadlock when calling wake_up() in
__kfence_alloc(), because we may already hold base->lock. This can happen
if debug objects are enabled:
...
__kfence_alloc+0xa0/0xbc0 mm/kfence/core.c:710
kfence_alloc include/linux/kfence.h:108 [inline]
...
kmem_cache_zalloc include/linux/slab.h:672 [inline]
fill_pool+0x264/0x5c0 lib/debugobjects.c:171
__debug_object_init+0x7a/0xd10 lib/debugobjects.c:560
debug_object_init lib/debugobjects.c:615 [inline]
debug_object_activate+0x32c/0x3e0 lib/debugobjects.c:701
debug_timer_activate kernel/time/timer.c:727 [inline]
__mod_timer+0x77d/0xe30 kernel/time/timer.c:1048
...
Therefore, switch to an open-coded wait loop. The difference to before is
that the waiter wakes up and rechecks the condition after 1 jiffy;
however, given the infrequency of kfence allocations, the difference is
insignificant.
Link: https://lkml.kernel.org/r/000000000000c0645805b7f982e4@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20210104130749.1768991-1-elver@xxxxxxxxxx
Reported-by: syzbot+8983d6d4f7df556be565@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Suggested-by: Hillf Danton <hdanton@xxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kfence/core.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
--- a/mm/kfence/core.c~mm-add-kernel-electric-fence-infrastructure-fix-3
+++ a/mm/kfence/core.c
@@ -94,9 +94,6 @@ DEFINE_STATIC_KEY_FALSE(kfence_allocatio
/* Gates the allocation, ensuring only one succeeds in a given period. */
static atomic_t allocation_gate = ATOMIC_INIT(1);
-/* Wait queue to wake up allocation-gate timer task. */
-static DECLARE_WAIT_QUEUE_HEAD(allocation_wait);
-
/* Statistics counters for debugfs. */
enum kfence_counter_id {
KFENCE_COUNTER_ALLOCATED,
@@ -582,6 +579,8 @@ late_initcall(kfence_debugfs_init);
static struct delayed_work kfence_timer;
static void toggle_allocation_gate(struct work_struct *work)
{
+ unsigned long end_wait;
+
if (!READ_ONCE(kfence_enabled))
return;
@@ -592,7 +591,14 @@ static void toggle_allocation_gate(struc
* Await an allocation. Timeout after 1 second, in case the kernel stops
* doing allocations, to avoid stalling this worker task for too long.
*/
- wait_event_timeout(allocation_wait, atomic_read(&allocation_gate) != 0, HZ);
+ end_wait = jiffies + HZ;
+ do {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ if (atomic_read(&allocation_gate) != 0)
+ break;
+ schedule_timeout(1);
+ } while (time_before(jiffies, end_wait));
+ __set_current_state(TASK_RUNNING);
/* Disable static key and reset timer. */
static_branch_disable(&kfence_allocation_key);
@@ -703,7 +709,6 @@ void *__kfence_alloc(struct kmem_cache *
*/
if (atomic_read(&allocation_gate) || atomic_inc_return(&allocation_gate) > 1)
return NULL;
- wake_up(&allocation_wait);
if (!READ_ONCE(kfence_enabled))
return NULL;
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
mm-add-kernel-electric-fence-infrastructure-fix.patch
mm-add-kernel-electric-fence-infrastructure-fix-2.patch
mm-add-kernel-electric-fence-infrastructure-fix-3.patch
arm64-kfence-enable-kfence-for-arm64.patch
kfence-use-pt_regs-to-generate-stack-trace-on-faults.patch
kfence-documentation-add-kfence-documentation.patch
kfence-add-test-suite.patch
kfence-add-test-suite-fix.patch
maintainers-add-entry-for-kfence.patch
