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* [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings
@ 2021-04-04 16:31 Vaibhav Jain
  2021-04-04 17:05 ` Christophe Leroy
  2021-04-19  3:59 ` Michael Ellerman
  0 siblings, 2 replies; 3+ messages in thread
From: Vaibhav Jain @ 2021-04-04 16:31 UTC (permalink / raw)
  To: linuxppc-dev, linux-nvdimm
  Cc: Santosh Sivaraj, Aneesh Kumar K . V, Vaibhav Jain, Dan Williams,
	Ira Weiny

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@linux.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>

---
Changelog:

v2: Issue cond_resched() every HZ jiffies instead of each iteration of
    the loop. [ Christophe Leroy ]
---
 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 581b20a2feaf..286e7e8cb919 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -338,7 +338,7 @@ 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;
@@ -351,8 +351,19 @@ 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


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings
  2021-04-04 16:31 [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings Vaibhav Jain
@ 2021-04-04 17:05 ` Christophe Leroy
  2021-04-19  3:59 ` Michael Ellerman
  1 sibling, 0 replies; 3+ messages in thread
From: Christophe Leroy @ 2021-04-04 17:05 UTC (permalink / raw)
  To: Vaibhav Jain, linuxppc-dev, linux-nvdimm
  Cc: Aneesh Kumar K . V, Dan Williams, Ira Weiny, Santosh Sivaraj



Le 04/04/2021 à 18:31, Vaibhav Jain a écrit :
> 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@linux.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> 
> ---
> Changelog:
> 
> v2: Issue cond_resched() every HZ jiffies instead of each iteration of
>      the loop. [ Christophe Leroy ]
> ---
>   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 581b20a2feaf..286e7e8cb919 100644
> --- a/arch/powerpc/mm/book3s64/hash_utils.c
> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
> @@ -338,7 +338,7 @@ 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;
> @@ -351,8 +351,19 @@ 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;
> 

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings
  2021-04-04 16:31 [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings Vaibhav Jain
  2021-04-04 17:05 ` Christophe Leroy
@ 2021-04-19  3:59 ` Michael Ellerman
  1 sibling, 0 replies; 3+ messages in thread
From: Michael Ellerman @ 2021-04-19  3:59 UTC (permalink / raw)
  To: Vaibhav Jain, linux-nvdimm, linuxppc-dev; +Cc: Aneesh Kumar K . V

On Sun, 4 Apr 2021 22:01:48 +0530, Vaibhav Jain wrote:
> 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
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/mm: Add cond_resched() while removing hpte mappings
      https://git.kernel.org/powerpc/c/a5d6a3e73acbd619dd5b7b831762b755f9e2db80

cheers

^ permalink raw reply	[flat|nested] 3+ messages in thread

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2021-04-04 16:31 [PATCH v2] powerpc/mm: Add cond_resched() while removing hpte mappings Vaibhav Jain
2021-04-04 17:05 ` Christophe Leroy
2021-04-19  3:59 ` Michael Ellerman

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