[tip:perf/core] perf sched replay: Fix the segmentation fault problem caused by pr_err in threads

[tip-bot for Yunlong Song]

Commit-ID:  08097abc11bcee21355dd857852a807b2a30b79f
Gitweb:     http://git.kernel.org/tip/08097abc11bcee21355dd857852a807b2a30b79f
Author:     Yunlong Song <yunlong.song@xxxxxxxxxx>
AuthorDate: Tue, 31 Mar 2015 21:46:32 +0800
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Wed, 8 Apr 2015 09:07:24 -0300

perf sched replay: Fix the segmentation fault problem caused by pr_err in threads

The pr_err in self_open_counters() prints error message to stderr.
Unlike stdout, stderr uses memory buffer on the stack of each calling
process.

The pr_err in self_open_counters() works in a thread called thread_func
created in function create_tasks, which concurrently creates
sched->nr_tasks threads.

If the error happens and pr_err prints the error message in each of
these threads, the stack size of the perf process (default is 8192
kbytes) will quickly run out and the segmentation fault will happen
then.

To solve this problem, pr_err with self_open_counters() should be moved
from newly created threads to the old main thread of the perf process.
Then the pr_err can work in a stable situation without the strange
segmentation fault problem.

Example:

Test environment: x86_64 with 160 cores

Before this patch:

 $ perf sched replay
 ...
 task   1549 (             :163132:    163132), nr_events: 1
 task   1550 (             :163540:    163540), nr_events: 1
 task   1551 (           <unknown>:         0), nr_events: 10
 Segmentation fault

After this patch:

 $ perf sched replay
 ...
 task   1549 (             :163132:    163132), nr_events: 1
 task   1550 (             :163540:    163540), nr_events: 1
 task   1551 (           <unknown>:         0), nr_events: 10
 ...

As shown above, the result continues without any segmentation fault.

Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1427809596-29559-6-git-send-email-yunlong.song@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/builtin-sched.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index dd71481..7fe3b3c 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -472,6 +472,7 @@ static u64 get_cpu_usage_nsec_self(int fd)
 struct sched_thread_parms {
 	struct task_desc  *task;
 	struct perf_sched *sched;
+	int fd;
 };
 
 static void *thread_func(void *ctx)
@@ -482,13 +483,12 @@ static void *thread_func(void *ctx)
 	u64 cpu_usage_0, cpu_usage_1;
 	unsigned long i, ret;
 	char comm2[22];
-	int fd;
+	int fd = parms->fd;
 
 	zfree(&parms);
 
 	sprintf(comm2, ":%s", this_task->comm);
 	prctl(PR_SET_NAME, comm2);
-	fd = self_open_counters();
 	if (fd < 0)
 		return NULL;
 again:
@@ -540,6 +540,7 @@ static void create_tasks(struct perf_sched *sched)
 		BUG_ON(parms == NULL);
 		parms->task = task = sched->tasks[i];
 		parms->sched = sched;
+		parms->fd = self_open_counters();
 		sem_init(&task->sleep_sem, 0, 0);
 		sem_init(&task->ready_for_work, 0, 0);
 		sem_init(&task->work_done_sem, 0, 0);
--
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