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From: Amol Grover <frextrite@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
	linux-kernel@vger.kernel.org,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: [Linux-kernel-mentees] [PATCH v2] callchain: Annotate RCU pointer with __rcu
Date: Thu, 30 Jan 2020 19:48:19 +0530	[thread overview]
Message-ID: <20200130141818.18391-1-frextrite@gmail.com> (raw)

Fixes following instances of sparse error
error: incompatible types in comparison expression
(different address spaces)
kernel/events/callchain.c:66:9: error: incompatible types in comparison
kernel/events/callchain.c:96:9: error: incompatible types in comparison
kernel/events/callchain.c:161:19: error: incompatible types in comparison

This introduces the following warning
kernel/events/callchain.c:65:17: warning: incorrect type in assignment
which is fixed as below

callchain_cpus_entries is annotated as an RCU pointer.
Hence rcu_dereference_protected or similar RCU API is
required to dereference the pointer.

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Squash both the commits into a single one.

 kernel/events/callchain.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index c2b41a263166..a672d02a1b3a 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -32,7 +32,7 @@ static inline size_t perf_callchain_entry__sizeof(void)
 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
 static atomic_t nr_callchain_events;
 static DEFINE_MUTEX(callchain_mutex);
-static struct callchain_cpus_entries *callchain_cpus_entries;
+static struct callchain_cpus_entries __rcu *callchain_cpus_entries;
 
 
 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
@@ -62,7 +62,8 @@ static void release_callchain_buffers(void)
 {
 	struct callchain_cpus_entries *entries;
 
-	entries = callchain_cpus_entries;
+	entries = rcu_dereference_protected(callchain_cpus_entries,
+					    lockdep_is_held(&callchain_mutex));
 	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
 	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
 }
-- 
2.24.1

_______________________________________________
Linux-kernel-mentees mailing list
Linux-kernel-mentees@lists.linuxfoundation.org
https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees

WARNING: multiple messages have this Message-ID (diff)
From: Amol Grover <frextrite@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org,
	Joel Fernandes <joel@joelfernandes.org>,
	Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Amol Grover <frextrite@gmail.com>
Subject: [PATCH v2] callchain: Annotate RCU pointer with __rcu
Date: Thu, 30 Jan 2020 19:48:19 +0530	[thread overview]
Message-ID: <20200130141818.18391-1-frextrite@gmail.com> (raw)

Fixes following instances of sparse error
error: incompatible types in comparison expression
(different address spaces)
kernel/events/callchain.c:66:9: error: incompatible types in comparison
kernel/events/callchain.c:96:9: error: incompatible types in comparison
kernel/events/callchain.c:161:19: error: incompatible types in comparison

This introduces the following warning
kernel/events/callchain.c:65:17: warning: incorrect type in assignment
which is fixed as below

callchain_cpus_entries is annotated as an RCU pointer.
Hence rcu_dereference_protected or similar RCU API is
required to dereference the pointer.

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
v2:
- Squash both the commits into a single one.

 kernel/events/callchain.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index c2b41a263166..a672d02a1b3a 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -32,7 +32,7 @@ static inline size_t perf_callchain_entry__sizeof(void)
 static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
 static atomic_t nr_callchain_events;
 static DEFINE_MUTEX(callchain_mutex);
-static struct callchain_cpus_entries *callchain_cpus_entries;
+static struct callchain_cpus_entries __rcu *callchain_cpus_entries;
 
 
 __weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
@@ -62,7 +62,8 @@ static void release_callchain_buffers(void)
 {
 	struct callchain_cpus_entries *entries;
 
-	entries = callchain_cpus_entries;
+	entries = rcu_dereference_protected(callchain_cpus_entries,
+					    lockdep_is_held(&callchain_mutex));
 	RCU_INIT_POINTER(callchain_cpus_entries, NULL);
 	call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
 }
-- 
2.24.1


             reply	other threads:[~2020-01-30 14:23 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-30 14:18 Amol Grover [this message]
2020-01-30 14:18 ` [PATCH v2] callchain: Annotate RCU pointer with __rcu Amol Grover
2020-02-14 18:20 ` [Linux-kernel-mentees] " Amol Grover
2020-02-14 18:20   ` Amol Grover

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