linux-kernel - [PATCH v2 0/3] mm/kmemleak: Avoid soft lockup in kmemleak

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Message-Id: <20220614220359.59282-1-longman@redhat.com>
Date:   Tue, 14 Jun 2022 18:03:56 -0400
From:   Waiman Long <longman@...hat.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v2 0/3] mm/kmemleak: Avoid soft lockup in kmemleak_scan()

 v2:
  - Update patch 3 to count the objects checked instead of being
    gray for determining when to do cond_resched(). This is more
    reliable.

There are 3 RCU-based object iteration loops in kmemleak_scan(). Because
of the need to take RCU read lock, we can't insert cond_resched() into
the loop like other parts of the function. As there can be millions of
objects to be scanned, it takes a while to iterate all of them. The
kmemleak functionality is usually enabled in a debug kernel which is
much slower than a non-debug kernel. With sufficient number of kmemleak
objects, the time to iterate them all may exceed 22s causing soft lockup.

  watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kmemleak:625]

This patch series make changes to the 3 object iteration loops in
kmemleak_scan() to prevent them from causing soft lockup.

Waiman Long (3):
  mm/kmemleak: Use _irq lock/unlock variants in kmemleak_scan/_clear()
  mm/kmemleak: Skip unlikely objects in kmemleak_scan() without taking
    lock
  mm/kmemleak: Prevent soft lockup in first object iteration loop of
    kmemleak_scan()

 mm/kmemleak.c | 60 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 49 insertions(+), 11 deletions(-)

-- 
2.31.1