[PATCH 1/4] perf lock contention: Track and show mmap_lock with address

[Namhyung Kim]

Sometimes there are severe contentions on the mmap_lock and we want
see it in the -l/--lock-addr output.  However it cannot symbolize
the mmap_lock because it's allocated dynamically without symbols.

Stephane and Hao gave me an idea separately to display mmap_lock by
following the current->mm pointer.  I added a flag to mark mmap_lock
after comparing the lock address so that it can show them differently.
With this change it can show mmap_lock like below:

  $ sudo ./perf lock con -abl -- sleep 10
   contended   total wait     max wait     avg wait            address   symbol
   ...
       16344    312.30 ms      2.22 ms     19.11 us   ffff8cc702595640
       17686    310.08 ms      1.49 ms     17.53 us   ffff8cc7025952c0
           3     84.14 ms     45.79 ms     28.05 ms   ffff8cc78114c478   mmap_lock
        3557     76.80 ms     68.75 us     21.59 us   ffff8cc77ca3af58
           1     68.27 ms     68.27 ms     68.27 ms   ffff8cda745dfd70
           9     54.53 ms      7.96 ms      6.06 ms   ffff8cc7642a48b8   mmap_lock
       14629     44.01 ms     60.00 us      3.01 us   ffff8cc7625f9ca0
        3481     42.63 ms    140.71 us     12.24 us   ffffffff937906ac   vmap_area_lock
       16194     38.73 ms     42.15 us      2.39 us   ffff8cd397cbc560
          11     38.44 ms     10.39 ms      3.49 ms   ffff8ccd6d12fbb8   mmap_lock
           1      5.43 ms      5.43 ms      5.43 ms   ffff8cd70018f0d8
        1674      5.38 ms    422.93 us      3.21 us   ffffffff92e06080   tasklist_lock
         581      4.51 ms    130.68 us      7.75 us   ffff8cc9b1259058
           5      3.52 ms      1.27 ms    703.23 us   ffff8cc754510070
         112      3.47 ms     56.47 us     31.02 us   ffff8ccee38b3120
         381      3.31 ms     73.44 us      8.69 us   ffffffff93790690   purge_vmap_area_lock
         255      3.19 ms     36.35 us     12.49 us   ffff8d053ce30c80

Note that mmap_lock was renamed some time ago and it needs to support
old kernels with a different name 'mmap_sem'.

Suggested-by: Stephane Eranian <eranian@xxxxxxxxxx>
Suggested-by: Hao Luo <haoluo@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/builtin-lock.c                     |  2 +-
 .../perf/util/bpf_skel/lock_contention.bpf.c  | 41 +++++++++++++++++++
 tools/perf/util/bpf_skel/lock_data.h          |  6 +++
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
index 054997edd98b..c62f4d9363a6 100644
--- a/tools/perf/builtin-lock.c
+++ b/tools/perf/builtin-lock.c
@@ -1663,7 +1663,7 @@ static void print_contention_result(struct lock_contention *con)
 			break;
 		case LOCK_AGGR_ADDR:
 			pr_info("  %016llx   %s\n", (unsigned long long)st->addr,
-				st->name ? : "");
+				(st->flags & LCD_F_MMAP_LOCK) ? "mmap_lock" : st->name);
 			break;
 		default:
 			break;
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index e6007eaeda1a..f092a78ae2b5 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -92,6 +92,14 @@ struct rw_semaphore___new {
 	atomic_long_t owner;
 } __attribute__((preserve_access_index));
 
+struct mm_struct___old {
+	struct rw_semaphore mmap_sem;
+} __attribute__((preserve_access_index));
+
+struct mm_struct___new {
+	struct rw_semaphore mmap_lock;
+} __attribute__((preserve_access_index));
+
 /* control flags */
 int enabled;
 int has_cpu;
@@ -204,6 +212,36 @@ static inline struct task_struct *get_lock_owner(__u64 lock, __u32 flags)
 	return task;
 }
 
+static inline __u32 check_lock_type(__u64 lock, __u32 flags)
+{
+	struct task_struct *curr;
+	struct mm_struct___old *mm_old;
+	struct mm_struct___new *mm_new;
+
+	switch (flags) {
+	case LCB_F_READ:  /* rwsem */
+	case LCB_F_WRITE:
+		curr = bpf_get_current_task_btf();
+		if (curr->mm == NULL)
+			break;
+		mm_new = (void *)curr->mm;
+		if (bpf_core_field_exists(mm_new->mmap_lock)) {
+			if (&mm_new->mmap_lock == (void *)lock)
+				return LCD_F_MMAP_LOCK;
+			break;
+		}
+		mm_old = (void *)curr->mm;
+		if (bpf_core_field_exists(mm_old->mmap_sem)) {
+			if (&mm_old->mmap_sem == (void *)lock)
+				return LCD_F_MMAP_LOCK;
+		}
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
 SEC("tp_btf/contention_begin")
 int contention_begin(u64 *ctx)
 {
@@ -314,6 +352,9 @@ int contention_end(u64 *ctx)
 			.flags = pelem->flags,
 		};
 
+		if (aggr_mode == LOCK_AGGR_ADDR)
+			first.flags |= check_lock_type(pelem->lock, pelem->flags);
+
 		bpf_map_update_elem(&lock_stat, &key, &first, BPF_NOEXIST);
 		bpf_map_delete_elem(&tstamp, &pid);
 		return 0;
diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
index 3d35fd4407ac..789f20833798 100644
--- a/tools/perf/util/bpf_skel/lock_data.h
+++ b/tools/perf/util/bpf_skel/lock_data.h
@@ -15,6 +15,12 @@ struct contention_task_data {
 	char comm[TASK_COMM_LEN];
 };
 
+/*
+ * Upper bits of the flags in the contention_data are used to identify
+ * some well-known locks which do not have symbols (non-global locks).
+ */
+#define LCD_F_MMAP_LOCK  (1U << 31)
+
 struct contention_data {
 	u64 total_time;
 	u64 min_time;
-- 
2.40.0.rc1.284.g88254d51c5-goog