From cd8dd032f61abeb08d2c03bab4968a9de231a1be Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Tue, 18 Jul 2017 20:20:19 -0300 Subject: [PATCH] perf cgroup: Fix refcount usage 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 Acked-by: Elena Reshetova Cc: Alexander Shishkin Cc: David Ahern Cc: David Carrillo-Cisneros Cc: Kees Kook Cc: Krister Johansen Cc: Paul Turner Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Sudeep Holla Cc: Thomas-Mich Richter Cc: Wang Nan 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 --- 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; } -- 2.30.2