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FROMGIT: kfence: fix potential deadlock due to wake_up()

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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@google.com
Link: https://lkml.kernel.org/r/20210104130749.1768991-1-elver@google.com
Reported-by: syzbot+8983d6d4f7df556be565@syzkaller.appspotmail.com
Signed-off-by: Marco Elver <elver@google.com>
Suggested-by: Hillf Danton <hdanton@sina.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Bug: 177201466
(cherry picked from commit c5fb1ab1a3c6d0ee02d1054a10d51ffcac57aed5
    https://github.com/hnaz/linux-mm v5.11-rc4-mmots-2021-01-21-20-10)
Test: CONFIG_KFENCE_KUNIT_TEST=y passes on Cuttlefish
Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: Iee40e9f216afbc3fce8e43c0e2a4bc807fdddf39
This commit is contained in:
Marco Elver 2021-01-22 09:18:33 +00:00 committed by Alistair Delva
parent ad318a7b61
commit 97d9142889
1 changed files with 10 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
mm/kfence/core.c
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@ -94,9 +94,6 @@ DEFINE_STATIC_KEY_FALSE(kfence_allocation_key);
/* 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(struct work_struct *work)
* 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 *s, size_t size, gfp_t flags)
*/
if (atomic_read(&allocation_gate) || atomic_inc_return(&allocation_gate) > 1)
return NULL;
wake_up(&allocation_wait);
if (!READ_ONCE(kfence_enabled))
return NULL;