On 6/11/21 7:17 PM, Xu, Yanfei wrote:
On 6/11/21 4:59 PM, Catalin Marinas wrote:
[Please note: This e-mail is from an EXTERNAL e-mail address]
On Wed, Jun 09, 2021 at 11:56:57PM +0800, Yanfei Xu wrote:
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.
I'm ok with READ_ONCE but your patch introduces functional changes.
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 92a2d4885808..5ccf3969b7fe 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1567,7 +1567,7 @@ static int kmemleak_scan_thread(void *arg)
}
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 file
*file, const char __user *user_buf,
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);
For symmetry, I'd add a WRITE_ONCE here as well.
- start_scan_thread();
- }
The reason for stop/start_scan_thread() wasn't to protect against
jiffies_scan_wait access but rather to force a new delay. Let's say you
start by default with a 10min delay between scans (default) but you want
to lower it to 1min. With the above removal of stop/start, you'd still
have to wait for 10min until the scanning thread will notice the change.
Also, with secs=0, the expectations is that the thread won't be
restarted but this is removed by your patch.
I see.
Thanks for your explain and sorry for my bad introduction. Will send a v2.
Hi Catalin and Andrew,
I sent the v2 patch which is renamed to:
[PATCH] mm/kmemleak: fix the possible wrong memory scanning period
I have tested it on qemux86, and hope you can help to review. Thanks.
--Yanfei
Thanks,
Yanfei
--
Catalin
