+ mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm/kmemleak: use READ_ONCE() for accessing jiffies_scan_wait
has been added to the -mm tree.  Its filename is
     mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Yanfei Xu <yanfei.xu@windriver.com>
Subject: mm/kmemleak: use READ_ONCE() for accessing jiffies_scan_wait

The stop_scan_thread() and start_scan_thread() cannot really solve the
problem of concurrent accessing the global jiffies_scan_wait.

kmemleak_write              kmemleak_scan_thread
                              while (!kthread_should_stop())
  stop_scan_thread
  jiffies_scan_wait = xxx       timeout = jiffies_scan_wait
  start_scan_thread

We could replace these with a READ_ONCE() when reading jiffies_scan_wait. 
It also can prevent compiler from reordering the jiffies_scan_wait which
is in while loop.

Link: https://lkml.kernel.org/r/20210609155657.26972-1-yanfei.xu@windriver.com
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kmemleak.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/mm/kmemleak.c~mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait
+++ a/mm/kmemleak.c
@@ -1567,7 +1567,7 @@ static int kmemleak_scan_thread(void *ar
 	}
 
 	while (!kthread_should_stop()) {
-		signed long timeout = jiffies_scan_wait;
+		signed long timeout = READ_ONCE(jiffies_scan_wait);
 
 		mutex_lock(&scan_mutex);
 		kmemleak_scan();
@@ -1812,11 +1812,8 @@ static ssize_t kmemleak_write(struct fil
 		ret = kstrtoul(buf + 5, 0, &secs);
 		if (ret < 0)
 			goto out;
-		stop_scan_thread();
-		if (secs) {
+		if (secs)
 			jiffies_scan_wait = msecs_to_jiffies(secs * 1000);
-			start_scan_thread();
-		}
 	} else if (strncmp(buf, "scan", 4) == 0)
 		kmemleak_scan();
 	else if (strncmp(buf, "dump=", 5) == 0)
_

Patches currently in -mm which might be from yanfei.xu@windriver.com are

mm-kmemleak-use-read_once-for-accessing-jiffies_scan_wait.patch