[PATCH v4 03/10] sched: snapshot thread flags

From: Mark Rutland
Date: Tue Aug 03 2021 - 05:55:47 EST

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

The READ_ONCE(ti->flags) .. cmpxchg(ti->flags) loop in
set_nr_if_polling() is left as-is for clarity.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2d9ff40f4661..bbce979c513d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8157,7 +8157,7 @@ void sched_show_task(struct task_struct *p)
pr_cont(" stack:%5lu pid:%5d ppid:%6d flags:0x%08lx\n",
free, task_pid_nr(p), ppid,
- (unsigned long)task_thread_info(p)->flags);
+ read_task_thread_flags(p));

print_worker_info(KERN_INFO, p);
print_stop_info(KERN_INFO, p);