lkml.org 
[lkml]   [2017]   [Apr]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] kthread: Fix race condition between kthread_parkme() and kthread_unpark()
Date
In general, if kthread_unpark() and kthread_parkme() execute together,
the kthread is supposed to be in an unparked state. This is because
kthread_unpark() either wakes up the thread if it already got parked,
or it cancels a prior kthread_park() call and hence renders the
kthread_parkme() moot.

However, if kthread_unpark() happens to execute between the time that
kthread_parkme() checks the KTHREAD_SHOULD_STOP flag and sets the
KTHREAD_IS_PARKED flag, then kthread_unpark() will not wake up the
thread and it will remain in a parked state.

This is fixed by making the checking of KTHREAD_SHOULD_STOP and the
setting of KTHREAD_IS_PARKED atomic via a cmpxchg inside kthread_parkme.

Signed-off-by: Junaid Shahid <junaids@google.com>
---
kernel/kthread.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 26db528c1d88..651f03baf62f 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -169,12 +169,20 @@ void *kthread_probe_data(struct task_struct *task)

static void __kthread_parkme(struct kthread *self)
{
+ ulong flags;
+
__set_current_state(TASK_PARKED);
- while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
- if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
- complete(&self->parked);
- schedule();
+ flags = self->flags;
+
+ while (test_bit(KTHREAD_SHOULD_PARK, &flags)) {
+ if (cmpxchg(&self->flags, flags,
+ flags | (1 << KTHREAD_IS_PARKED)) == flags) {
+ if (!test_bit(KTHREAD_IS_PARKED, &flags))
+ complete(&self->parked);
+ schedule();
+ }
__set_current_state(TASK_PARKED);
+ flags = self->flags;
}
clear_bit(KTHREAD_IS_PARKED, &self->flags);
__set_current_state(TASK_RUNNING);
--
2.13.0.rc0.306.g87b477812d-goog
\
 
 \ /
  Last update: 2017-04-29 04:33    [W:0.103 / U:0.212 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site