Commit 593889c4 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Boqun Feng
Browse files

srcu: Don't queue workqueue handlers to never-online CPUs 



While an srcu_struct structure is in the midst of switching from CPU-0
to all-CPUs state, it can attempt to invoke callbacks for CPUs that
have never been online.  Worse yet, it can attempt in invoke callbacks
for CPUs that never will be online, even including imaginary CPUs not in
cpu_possible_mask.  This can cause hangs on s390, which is not set up to
deal with workqueue handlers being scheduled on such CPUs.  This commit
therefore causes Tree SRCU to refrain from queueing workqueue handlers
on CPUs that have not yet (and might never) come online.

Because callbacks are not invoked on CPUs that have not been
online, it is an error to invoke call_srcu(), synchronize_srcu(), or
synchronize_srcu_expedited() on a CPU that is not yet fully online.
However, it turns out to be less code to redirect the callbacks
from too-early invocations of call_srcu() than to warn about such
invocations.  This commit therefore also redirects callbacks queued on
not-yet-fully-online CPUs to the boot CPU.

Reported-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Fixes: 61bbcfb5 ("srcu: Push srcu_node allocation to GP when non-preemptible")
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Tested-by: default avatarVasily Gorbik <gor@linux.ibm.com>
Tested-by: default avatarSamir <samir@linux.ibm.com>
Reviewed-by: default avatarShrikanth Hegde <sshegde@linux.ibm.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarUladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: default avatarBoqun Feng <boqun@kernel.org>
parent 7fd2df20

kernel/rcu/srcutree.c

+6 −6
Original line number Diff line number Diff line
@@ -897,12 +897,10 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp 
{

	int cpu;



	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {

		if (!(mask & (1UL << (cpu - snp->grplo))))

			continue;

	for (cpu = snp->grplo; cpu <= snp->grphi; cpu++)

		if ((mask & (1UL << (cpu - snp->grplo))) && rcu_cpu_beenfullyonline(cpu))

			srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);

}

}



/*

 * Note the end of an SRCU grace period.  Initiates callback invocation
@@ -1322,7 +1320,9 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, 
	 */

	idx = __srcu_read_lock_nmisafe(ssp);

	ss_state = smp_load_acquire(&ssp->srcu_sup->srcu_size_state);

	if (ss_state < SRCU_SIZE_WAIT_CALL)

	// If !rcu_cpu_beenfullyonline(), interrupts are still disabled,

	// so no migration is possible in either direction from this CPU.

	if (ss_state < SRCU_SIZE_WAIT_CALL || !rcu_cpu_beenfullyonline(raw_smp_processor_id()))

		sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());

	else

		sdp = raw_cpu_ptr(ssp->sda);