[PATCH v2 4/4] lockdep: Add a boot parameter enabling to track page locks using lockdep and disable it by default

[Byungchul Park]

To track page locks using lockdep, we need a huge memory space for
lockdep_map per page. So, it would be better to make it disabled by
default and provide a boot parameter to turn it on. Do it.

Suggested-by: Michal Hocko 
Signed-off-by: Byungchul Park 
---
 Documentation/admin-guide/kernel-parameters.txt |  7 +++
 lib/Kconfig.debug   |  5 -
 mm/filemap.c| 23 +++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index f20ed5e..5e8d15d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -712,6 +712,13 @@
crossrelease_fullstack
[KNL] Allow to record full stack trace in cross-release
 
+   lockdep_pagelock=
+   [KNL] Boot-time lockdep_pagelock enabling option.
+   Storage of lockdep_map per page to track lock_page()/
+   unlock_page() is disabled by default. With this switch,
+   we can turn it on.
+   on: enable the feature
+
cryptomgr.notests
 [KNL] Disable crypto self-tests
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 45fdb3a..c609e97 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1185,7 +1185,10 @@ config LOCKDEP_PAGELOCK
select PAGE_EXTENSION
help
 PG_locked lock is a kind of crosslock. Using crossrelease feature,
-PG_locked lock can work with lockdep.
+PG_locked lock can work with lockdep. Even if you include this
+feature on your build, it is disabled in default. You should pass
+"lockdep_pagelock=on" to boot parameter in order to enable it. It
+consumes a fair amount of memory if enabled.
 
 config BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK
bool "Enable the boot parameter, crossrelease_fullstack"
diff --git a/mm/filemap.c b/mm/filemap.c
index 34251fb..cb7b20b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1231,8 +1231,24 @@ int __lock_page_or_retry(struct page *page, struct 
mm_struct *mm,
 
 #ifdef CONFIG_LOCKDEP_PAGELOCK
 
+static int lockdep_pagelock;
+static int __init allow_lockdep_pagelock(char *str)
+{
+   if (!str)
+   return -EINVAL;
+
+   if (!strcmp(str, "on"))
+   lockdep_pagelock = 1;
+
+   return 0;
+}
+early_param("lockdep_pagelock", allow_lockdep_pagelock);
+
 static bool need_lockdep_pagelock(void)
 {
+   if (!lockdep_pagelock)
+   return false;
+
return true;
 }
 
@@ -1286,6 +1302,10 @@ static void init_zones_in_node(pg_data_t *pgdat)
 static void init_lockdep_pagelock(void)
 {
pg_data_t *pgdat;
+
+   if (!lockdep_pagelock)
+   return;
+
for_each_online_pgdat(pgdat)
init_zones_in_node(pgdat);
 }
@@ -1305,6 +1325,9 @@ struct lockdep_map *get_page_map(struct page *p)
 {
struct page_ext *e;
 
+   if (!lockdep_pagelock)
+   return NULL;
+
e = lookup_page_ext(p);
if (!e)
return NULL;
-- 
1.9.1

[PATCH v2 4/4] lockdep: Add a boot parameter enabling to track page locks using lockdep and disable it by default

[Byungchul Park]

To track page locks using lockdep, we need a huge memory space for
lockdep_map per page. So, it would be better to make it disabled by
default and provide a boot parameter to turn it on. Do it.

Suggested-by: Michal Hocko 
Signed-off-by: Byungchul Park 
---
 Documentation/admin-guide/kernel-parameters.txt |  7 +++
 lib/Kconfig.debug   |  5 -
 mm/filemap.c| 23 +++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index f20ed5e..5e8d15d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -712,6 +712,13 @@
crossrelease_fullstack
[KNL] Allow to record full stack trace in cross-release
 
+   lockdep_pagelock=
+   [KNL] Boot-time lockdep_pagelock enabling option.
+   Storage of lockdep_map per page to track lock_page()/
+   unlock_page() is disabled by default. With this switch,
+   we can turn it on.
+   on: enable the feature
+
cryptomgr.notests
 [KNL] Disable crypto self-tests
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 45fdb3a..c609e97 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1185,7 +1185,10 @@ config LOCKDEP_PAGELOCK
select PAGE_EXTENSION
help
 PG_locked lock is a kind of crosslock. Using crossrelease feature,
-PG_locked lock can work with lockdep.
+PG_locked lock can work with lockdep. Even if you include this
+feature on your build, it is disabled in default. You should pass
+"lockdep_pagelock=on" to boot parameter in order to enable it. It
+consumes a fair amount of memory if enabled.
 
 config BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK
bool "Enable the boot parameter, crossrelease_fullstack"
diff --git a/mm/filemap.c b/mm/filemap.c
index 34251fb..cb7b20b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1231,8 +1231,24 @@ int __lock_page_or_retry(struct page *page, struct 
mm_struct *mm,
 
 #ifdef CONFIG_LOCKDEP_PAGELOCK
 
+static int lockdep_pagelock;
+static int __init allow_lockdep_pagelock(char *str)
+{
+   if (!str)
+   return -EINVAL;
+
+   if (!strcmp(str, "on"))
+   lockdep_pagelock = 1;
+
+   return 0;
+}
+early_param("lockdep_pagelock", allow_lockdep_pagelock);
+
 static bool need_lockdep_pagelock(void)
 {
+   if (!lockdep_pagelock)
+   return false;
+
return true;
 }
 
@@ -1286,6 +1302,10 @@ static void init_zones_in_node(pg_data_t *pgdat)
 static void init_lockdep_pagelock(void)
 {
pg_data_t *pgdat;
+
+   if (!lockdep_pagelock)
+   return;
+
for_each_online_pgdat(pgdat)
init_zones_in_node(pgdat);
 }
@@ -1305,6 +1325,9 @@ struct lockdep_map *get_page_map(struct page *p)
 {
struct page_ext *e;
 
+   if (!lockdep_pagelock)
+   return NULL;
+
e = lookup_page_ext(p);
if (!e)
return NULL;
-- 
1.9.1