[PATCH v18 38/42] rcu/update: fix same dept key collision between various types of RCU

[Byungchul Park <byungchul@sk.com>]

From: Yunseong Kim <ysk@kzalloc.com>

The current implementation shares the same dept key for multiple
synchronization points, which can lead to false positive reports in
dependency tracking and potential confusion in debugging.  For example,
both normal RCU and tasks trace RCU synchronization points use the same
dept key.  Specifically:

   1. synchronize_rcu() uses a dept key embedded in __wait_rcu_gp():

      synchronize_rcu()
         synchronize_rcu_normal()
            _wait_rcu_gp()
               __wait_rcu_gp() <- the key as static variable

   2. synchronize_rcu_tasks_trace() uses the dept key, too:

      synchronize_rcu_tasks_trace()
         synchronize_rcu_tasks_generic()
            _wait_rcu_gp()
               __wait_rcu_gp() <- the key as static variable

Since the both rely on the same dept key, dept may report false positive
circular dependency.  To resolve this, separate dept keys and maps
should be assigned to each struct rcu_synchronize.

   ===================================================
   DEPT: Circular dependency has been detected.
   6.15.0-rc6-00042-ged94bafc6405 #2 Not tainted
   ---------------------------------------------------
   summary
   ---------------------------------------------------
   *** DEADLOCK ***

   context A
      [S] lock(cpu_hotplug_lock:0)
      [W] __wait_rcu_gp(<sched>:0)
      [E] unlock(cpu_hotplug_lock:0)

   context B
      [S] (unknown)(<sched>:0)
      [W] lock(cpu_hotplug_lock:0)
      [E] try_to_wake_up(<sched>:0)

   [S]: start of the event context
   [W]: the wait blocked
   [E]: the event not reachable
   ---------------------------------------------------
   context A's detail
   ---------------------------------------------------
   context A
      [S] lock(cpu_hotplug_lock:0)
      [W] __wait_rcu_gp(<sched>:0)
      [E] unlock(cpu_hotplug_lock:0)

   [S] lock(cpu_hotplug_lock:0):
   [<ffff8000802ce964>] cpus_read_lock+0x14/0x20
   stacktrace:
         percpu_down_read.constprop.0+0x88/0x2ec
         cpus_read_lock+0x14/0x20
         cgroup_procs_write_start+0x164/0x634
         __cgroup_procs_write+0xdc/0x4d0
         cgroup_procs_write+0x34/0x74
         cgroup_file_write+0x25c/0x670
         kernfs_fop_write_iter+0x2ec/0x498
         vfs_write+0x574/0xc30
         ksys_write+0x124/0x244
         __arm64_sys_write+0x70/0xa4
         invoke_syscall+0x88/0x2e0
         el0_svc_common.constprop.0+0xe8/0x2e0
         do_el0_svc+0x44/0x60
         el0_svc+0x50/0x188
         el0t_64_sync_handler+0x10c/0x140
         el0t_64_sync+0x198/0x19c

   [W] __wait_rcu_gp(<sched>:0):
   [<ffff8000804ce88c>] __wait_rcu_gp+0x324/0x498
   stacktrace:
         schedule+0xcc/0x348
         schedule_timeout+0x1a4/0x268
         __wait_for_common+0x1c4/0x3f0
         __wait_for_completion_state+0x20/0x38
         __wait_rcu_gp+0x35c/0x498
         synchronize_rcu_normal+0x200/0x218
         synchronize_rcu+0x234/0x2a0
         rcu_sync_enter+0x11c/0x300
         percpu_down_write+0xb4/0x3e0
         cgroup_procs_write_start+0x174/0x634
         __cgroup_procs_write+0xdc/0x4d0
         cgroup_procs_write+0x34/0x74
         cgroup_file_write+0x25c/0x670
         kernfs_fop_write_iter+0x2ec/0x498
         vfs_write+0x574/0xc30
         ksys_write+0x124/0x244

   [E] unlock(cpu_hotplug_lock:0):
   (N/A)
   ---------------------------------------------------
   context B's detail
   ---------------------------------------------------
   context B
      [S] (unknown)(<sched>:0)
      [W] lock(cpu_hotplug_lock:0)
      [E] try_to_wake_up(<sched>:0)

   [S] (unknown)(<sched>:0):
   (N/A)

   [W] lock(cpu_hotplug_lock:0):
   [<ffff8000802ce964>] cpus_read_lock+0x14/0x20
   stacktrace:
         percpu_down_read.constprop.0+0x6c/0x2ec
         cpus_read_lock+0x14/0x20
         check_all_holdout_tasks_trace+0x90/0xa30
         rcu_tasks_wait_gp+0x47c/0x938
         rcu_tasks_one_gp+0x75c/0xef8
         rcu_tasks_kthread+0x180/0x1dc
         kthread+0x3ac/0x74c
         ret_from_fork+0x10/0x20

   [E] try_to_wake_up(<sched>:0):
   [<ffff8000804233b8>] complete+0xb8/0x1e8
   stacktrace:
         try_to_wake_up+0x374/0x1164
         complete+0xb8/0x1e8
         wakeme_after_rcu+0x14/0x20
         rcu_tasks_invoke_cbs+0x218/0xaa8
         rcu_tasks_one_gp+0x834/0xef8
         rcu_tasks_kthread+0x180/0x1dc
         kthread+0x3ac/0x74c
         ret_from_fork+0x10/0x20
   (wait to wake up)
   stacktrace:
         __schedule+0xf64/0x3614
         schedule+0xcc/0x348
         schedule_timeout+0x1a4/0x268
         __wait_for_common+0x1c4/0x3f0
         __wait_for_completion_state+0x20/0x38
         __wait_rcu_gp+0x35c/0x498
         synchronize_rcu_tasks_generic+0x14c/0x220
         synchronize_rcu_tasks_trace+0x24/0x8c
         rcu_init_tasks_generic+0x168/0x194
         do_one_initcall+0x174/0xa00
         kernel_init_freeable+0x744/0x7dc
         kernel_init+0x78/0x220
         ret_from_fork+0x10/0x20

Separating the dept key and map for each of struct rcu_synchronize,
ensuring proper tracking for each execution context.

Signed-off-by: Yunseong Kim <ysk@kzalloc.com>
[ Rewrote the changelog. ]
Signed-off-by: Byungchul Park <byungchul@sk.com>
---
 include/linux/rcupdate_wait.h | 13 ++++++++-----
 kernel/rcu/rcu.h              |  1 +
 kernel/rcu/update.c           |  5 +++--
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
index 4c92d4291cce..ee598e70b4bc 100644
--- a/include/linux/rcupdate_wait.h
+++ b/include/linux/rcupdate_wait.h
@@ -19,17 +19,20 @@ struct rcu_synchronize {
 
 	/* This is for debugging. */
 	struct rcu_gp_oldstate oldstate;
+	struct dept_map dmap;
+	struct dept_key dkey;
 };
 void wakeme_after_rcu(struct rcu_head *head);
 
 void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *crcu_array,
-		   struct rcu_synchronize *rs_array);
+		   struct rcu_synchronize *rs_array, struct dept_key *dkey);
 
 #define _wait_rcu_gp(checktiny, state, ...) \
-do {												\
-	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };					\
-	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];				\
-	__wait_rcu_gp(checktiny, state, ARRAY_SIZE(__crcu_array), __crcu_array, __rs_array);	\
+do {													\
+	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };						\
+	static struct dept_key __key;									\
+	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];					\
+	__wait_rcu_gp(checktiny, state, ARRAY_SIZE(__crcu_array), __crcu_array, __rs_array, &__key);	\
 } while (0)
 
 #define wait_rcu_gp(...) _wait_rcu_gp(false, TASK_UNINTERRUPTIBLE, __VA_ARGS__)
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 9cf01832a6c3..c0d8ea139596 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -12,6 +12,7 @@
 
 #include <linux/slab.h>
 #include <trace/events/rcu.h>
+#include <linux/dept_sdt.h>
 
 /*
  * Grace-period counter management.
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index dfeba9b35395..6b7ede219433 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -409,7 +409,7 @@ void wakeme_after_rcu(struct rcu_head *head)
 EXPORT_SYMBOL_GPL(wakeme_after_rcu);
 
 void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *crcu_array,
-		   struct rcu_synchronize *rs_array)
+		   struct rcu_synchronize *rs_array, struct dept_key *dkey)
 {
 	int i;
 	int j;
@@ -426,7 +426,8 @@ void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *c
 				break;
 		if (j == i) {
 			init_rcu_head_on_stack(&rs_array[i].head);
-			init_completion(&rs_array[i].completion);
+			sdt_map_init_key(&rs_array[i].dmap, dkey);
+			init_completion_dmap(&rs_array[i].completion, &rs_array[i].dmap);
 			(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
 		}
 	}
-- 
2.17.1