[PATCH 5.11 125/152] powerpc/pseries/mobility: handle premature return from H_JOIN

Greg Kroah-Hartman
2021-04-05T09:22:10Z

From: Nathan Lynch <nathanl@linux.ibm.com>

[ Upstream commit 274cb1ca2e7ce02cab56f5f4c61a74aeb566f931 ]

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: 9327dc0aeef3 ("powerpc/pseries/mobility: use stop_machine for join/suspend")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210315080045.460331-3-nathanl@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/platforms/pseries/mobility.c | 26 ++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
index a6739ce9feac..e83e0891272d 100644
--- a/arch/powerpc/platforms/pseries/mobility.c
+++ b/arch/powerpc/platforms/pseries/mobility.c
@@ -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);
--
2.30.2