Commit 274cb1ca authored by Nathan Lynch's avatar Nathan Lynch Committed by Michael Ellerman
Browse files

powerpc/pseries/mobility: handle premature return from H_JOIN 



The pseries join/suspend sequence in its current form was written with
the assumption that it was the only user of H_PROD and that it needn't
handle spurious successful returns from H_JOIN. That's wrong;
powerpc's paravirt spinlock code uses H_PROD, and CPUs entering
do_join() can be woken prematurely from H_JOIN with a status of
H_SUCCESS as a result. This causes all CPUs to exit the sequence
early, preventing suspend from occurring at all.

Add a 'done' boolean flag to the pseries_suspend_info struct, and have
the waking thread set it before waking the other threads. Threads
which receive H_SUCCESS from H_JOIN retry if the 'done' flag is still
unset.

Fixes: 9327dc0a ("powerpc/pseries/mobility: use stop_machine for join/suspend")
Signed-off-by: default avatarNathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210315080045.460331-3-nathanl@linux.ibm.com
parent e834df6c

arch/powerpc/platforms/pseries/mobility.c

+25 −1
Original line number Diff line number Diff line
@@ -458,9 +458,12 @@ static int do_suspend(void) 
 *           or if an error is received from H_JOIN. The thread which performs

 *           the first increment (i.e. sets it to 1) is responsible for

 *           waking the other threads.

 * @done: False if join/suspend is in progress. True if the operation is

 *        complete (successful or not).

 */

struct pseries_suspend_info {

	atomic_t counter;

	bool done;

};



static int do_join(void *arg)
@@ -470,6 +473,7 @@ static int do_join(void *arg) 
	long hvrc;

	int ret;



retry:

	/* Must ensure MSR.EE off for H_JOIN. */

	hard_irq_disable();

	hvrc = plpar_hcall_norets(H_JOIN);
@@ -485,8 +489,20 @@ static int do_join(void *arg) 
	case H_SUCCESS:

		/*

		 * The suspend is complete and this cpu has received a

		 * prod.

		 * prod, or we've received a stray prod from unrelated

		 * code (e.g. paravirt spinlocks) and we need to join

		 * again.

		 *

		 * This barrier orders the return from H_JOIN above vs

		 * the load of info->done. It pairs with the barrier

		 * in the wakeup/prod path below.

		 */

		smp_mb();

		if (READ_ONCE(info->done) == false) {

			pr_info_ratelimited("premature return from H_JOIN on CPU %i, retrying",

					    smp_processor_id());

			goto retry;

		}

		ret = 0;

		break;

	case H_BAD_MODE:
@@ -500,6 +516,13 @@ static int do_join(void *arg) 


	if (atomic_inc_return(counter) == 1) {

		pr_info("CPU %u waking all threads\n", smp_processor_id());

		WRITE_ONCE(info->done, true);

		/*

		 * This barrier orders the store to info->done vs subsequent

		 * H_PRODs to wake the other CPUs. It pairs with the barrier

		 * in the H_SUCCESS case above.

		 */

		smp_mb();

		prod_others();

	}

	/*
@@ -553,6 +576,7 @@ static int pseries_suspend(u64 handle) 


		info = (struct pseries_suspend_info) {

			.counter = ATOMIC_INIT(0),

			.done = false,

		};



		ret = stop_machine(do_join, &info, cpu_online_mask);