From: Frederic Weisbecker frederic@kernel.org
mainline inclusion from mainline-v6.3-rc4 commit b416514054810cf2d2cc348ae477cea619b64da7 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I9NZ3E
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id...
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RCU sometimes needs to perform a delayed wake up for specific kthreads handling offloaded callbacks (RCU_NOCB). These wakeups are performed by timers and upon entry to idle (also to guest and to user on nohz_full).
However the delayed wake-up on kernel exit is actually performed after the thread flags are fetched towards the fast path check for work to do on exit to user. As a result, and if there is no other pending work to do upon that kernel exit, the current task will resume to userspace with TIF_RESCHED set and the pending wake up ignored.
Fix this with fetching the thread flags _after_ the delayed RCU-nocb kthread wake-up.
Fixes: 47b8ff194c1f ("entry: Explicitly flush pending rcuog wakeup before last rescheduling point") Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Link: https://lore.kernel.org/r/20230315194349.10798-3-joel@joelfernandes.org Conflicts: kernel/entry/common.c [adapt for missing read_thread_flags()] Signed-off-by: Wei Li liwei391@huawei.com --- kernel/entry/common.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c index a028b28daed5..0796a85c9680 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -195,13 +195,14 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
static void exit_to_user_mode_prepare(struct pt_regs *regs) { - unsigned long ti_work = READ_ONCE(current_thread_info()->flags); + unsigned long ti_work;
lockdep_assert_irqs_disabled();
/* Flush pending rcuog wakeup before the last need_resched() check */ rcu_nocb_flush_deferred_wakeup();
+ ti_work = READ_ONCE(current_thread_info()->flags); if (unlikely(ti_work & EXIT_TO_USER_MODE_WORK)) ti_work = exit_to_user_mode_loop(regs, ti_work);