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Subject[PATCH 24/40] perf cgroup: Fix refcount usage
Date
From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>

When converting from atomic_t to refcount_t we didn't follow the usual
step of initializing it to one before taking any new reference, which
trips over checking if taking a reference for a freed refcount_t, fix
it.

Brendan's report:

---
It's 4.12-rc7, with node v4.4.1. I'm building 4.13-rc1 now, as I hit
what I think is another unrelated perf bug and I'm starting to wonder
what else is broken on that version:

(root) /mnt/src/linux-4.12-rc7/tools/perf # ./perf record -F 99 -a -e
cpu-clock --cgroup=docker/f9e9d5df065b14646e8a11edc837a13877fd90c171137b2ba3feb67a0201cb65
-g
perf: /mnt/src/linux-4.12-rc7/tools/include/linux/refcount.h:108:
refcount_inc: Assertion `!(!refcount_inc_not_zero(r))' failed.
Aborted

that used to work...
---

Testing it:

Before:

# perf stat -e cycles -C 0 --cgroup /
perf: /home/acme/git/linux/tools/include/linux/refcount.h:108: refcount_inc: Assertion `!(!refcount_inc_not_zero(r))' failed.
Aborted (core dumped)
#

After:

# perf stat -e cycles -C 0 --cgroup /
^C
Performance counter stats for 'CPU(s) 0':

132,081,393 cycles /

2.492942763 seconds time elapsed

#

Reported-by: Brendan Gregg <brendan.d.gregg@gmail.com>
Acked-by: Elena Reshetova <elena.reshetova@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: David Carrillo-Cisneros <davidcc@google.com>
Cc: Kees Kook <keescook@chromium.org>
Cc: Krister Johansen <kjlx@templeofstupid.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Sudeep Holla <Sudeep.Holla@arm.com>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 79c5fe6db8c7 ("perf cgroup: Convert cgroup_sel.refcnt from atomic_t to refcount_t")
Link: http://lkml.kernel.org/n/tip-l7ovfblq14ip2i08m1g0fkhv@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/cgroup.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/cgroup.c b/tools/perf/util/cgroup.c
index 03347748f3fa..0e77bc9e5f3c 100644
--- a/tools/perf/util/cgroup.c
+++ b/tools/perf/util/cgroup.c
@@ -98,8 +98,10 @@ static int add_cgroup(struct perf_evlist *evlist, char *str)
cgrp = counter->cgrp;
if (!cgrp)
continue;
- if (!strcmp(cgrp->name, str))
+ if (!strcmp(cgrp->name, str)) {
+ refcount_inc(&cgrp->refcnt);
break;
+ }

cgrp = NULL;
}
@@ -110,6 +112,7 @@ static int add_cgroup(struct perf_evlist *evlist, char *str)
return -1;

cgrp->name = str;
+ refcount_set(&cgrp->refcnt, 1);

cgrp->fd = open_cgroup(str);
if (cgrp->fd == -1) {
@@ -128,12 +131,11 @@ static int add_cgroup(struct perf_evlist *evlist, char *str)
goto found;
n++;
}
- if (refcount_read(&cgrp->refcnt) == 0)
+ if (refcount_dec_and_test(&cgrp->refcnt))
free(cgrp);

return -1;
found:
- refcount_inc(&cgrp->refcnt);
counter->cgrp = cgrp;
return 0;
}
--
2.9.4
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