[PATCH AUTOSEL 5.11 064/104] powerpc/mm: Add cond_resched() while removing hpte mappings

From: Sasha Levin
Date: Wed May 05 2021 - 12:51:56 EST


From: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>

[ Upstream commit a5d6a3e73acbd619dd5b7b831762b755f9e2db80 ]

While removing large number of mappings from hash page tables for
large memory systems as soft-lockup is reported because of the time
spent inside htap_remove_mapping() like one below:

watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
<snip>
NIP plpar_hcall+0x38/0x58
LR pSeries_lpar_hpte_invalidate+0x68/0xb0
Call Trace:
0x1fffffffffff000 (unreliable)
pSeries_lpar_hpte_removebolted+0x9c/0x230
hash__remove_section_mapping+0xec/0x1c0
remove_section_mapping+0x28/0x3c
arch_remove_memory+0xfc/0x150
devm_memremap_pages_release+0x180/0x2f0
devm_action_release+0x30/0x50
release_nodes+0x28c/0x300
device_release_driver_internal+0x16c/0x280
unbind_store+0x124/0x170
drv_attr_store+0x44/0x60
sysfs_kf_write+0x64/0x90
kernfs_fop_write+0x1b0/0x290
__vfs_write+0x3c/0x70
vfs_write+0xd4/0x270
ksys_write+0xdc/0x130
system_call+0x5c/0x70

Fix this by adding a cond_resched() to the loop in
htap_remove_mapping() that issues hcall to remove hpte mapping. The
call to cond_resched() is issued every HZ jiffies which should prevent
the soft-lockup from being reported.

Suggested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Signed-off-by: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>
Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210404163148.321346-1-vaibhav@xxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/powerpc/mm/book3s64/hash_utils.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 73b06adb6eeb..f81b09769e0b 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -337,7 +337,7 @@ int htab_bolt_mapping(unsigned long vstart, unsigned long vend,
int htab_remove_mapping(unsigned long vstart, unsigned long vend,
int psize, int ssize)
{
- unsigned long vaddr;
+ unsigned long vaddr, time_limit;
unsigned int step, shift;
int rc;
int ret = 0;
@@ -350,8 +350,19 @@ int htab_remove_mapping(unsigned long vstart, unsigned long vend,

/* Unmap the full range specificied */
vaddr = ALIGN_DOWN(vstart, step);
+ time_limit = jiffies + HZ;
+
for (;vaddr < vend; vaddr += step) {
rc = mmu_hash_ops.hpte_removebolted(vaddr, psize, ssize);
+
+ /*
+ * For large number of mappings introduce a cond_resched()
+ * to prevent softlockup warnings.
+ */
+ if (time_after(jiffies, time_limit)) {
+ cond_resched();
+ time_limit = jiffies + HZ;
+ }
if (rc == -ENOENT) {
ret = -ENOENT;
continue;
--
2.30.2