On Mon, Jan 11, 2021 at 01:40:14AM +0100, Frederic Weisbecker wrote:
On Sat, Jan 09, 2021 at 03:05:33AM +0100, Frederic Weisbecker wrote:
Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point on resuming to user mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling.
Signed-off-by: Frederic Weisbecker frederic@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnarmingo@kernel.org Cc: Paul E. McKenney paulmck@kernel.org Cc: Rafael J. Wysocki rafael.j.wysocki@intel.com
kernel/entry/common.c | 6 ++++++ kernel/rcu/tree.c | 12 +++++++----- 2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 378341642f94..8f3292b5f9b7 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -178,6 +178,9 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs, /* Architecture specific TIF work */ arch_exit_to_user_mode_work(regs, ti_work);
/* Check if any of the above work has queued a deferred wakeup */rcu_nocb_flush_deferred_wakeup();So this needs to be moved to the IRQs disabled section, just a few lines later, otherwise preemption may schedule another task that in turn do call_rcu() and create new deferred wake up (thank Paul for the warning). Not to mention moving to another CPU with its own deferred wakeups to flush...
I'll fix that for the next version.
Ah, so it was not just my laptop dying, then! ;-)
Thanx, Paul