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authorArnaldo Carvalho de Melo <acme@redhat.com>2019-07-05 18:11:35 +0300
committerArnaldo Carvalho de Melo <acme@redhat.com>2019-07-06 20:29:32 +0300
commit4c00af0e94cd01b8c5a5e6b3323d34677b04e192 (patch)
tree8a95cfb4207758bf4b88ae00da515f822df78b81 /tools/perf/util/machine.c
parentc952b35f4b15dd1b83e952718dec3307256383ef (diff)
downloadlinux-4c00af0e94cd01b8c5a5e6b3323d34677b04e192.tar.xz
perf thread: Allow references to thread objects after machine__exit()
Threads are created when we either synthesize PERF_RECORD_FORK events for pre-existing threads or when we receive PERF_RECORD_FORK events from the kernel as new threads get created. We then keep them in machine->threads[].entries rb trees till when we receive a PERF_RECORD_EXIT, i.e. that thread terminated. The thread object has a reference count that is grabbed when, for instance, we keep that thread referenced in struct hist_entry, in 'perf report' and 'perf top'. When we receive a PERF_RECORD_EXIT we remove the thread object from the rb tree and move it to the corresponding machine->threads[].dead list, then we do a thread__put(), dropping the reference we had for keeping it in the rb tree. In thread__put() we were assuming that when the reference count hit zero we should remove it from the dead list by simply doing a list_del_init(&thread->node). That works well when all the thread lifetime is during the machine that has the list heads lifetime, since we know that we can do the list_del_init() and it will update the 'dead' list_head. But in 'perf sched lat' we were doing: machine__new() (via perf_session__new) process events, grabbing refcounts to keep those thread objects in 'perf sched' local data structures. machine__exit() (via perf_session__delete) which would delete the 'dead' list heads. And then doing the final thread__put() for the refcounts 'perf sched' rightfully obtained for keeping those thread object references. b00m, since thread__put() would do the list_del_init() touching a dead dead list head. Fix it by removing all the dead threads from machine->threads[].dead at machine__exit(), since whatever is there should have refcounts taken by things like 'perf sched lat', and make thread__put() check if the thread is in a linked list before removing it from that list. Reported-by: Wei Li <liwei391@huawei.com> Link: https://lkml.kernel.org/r/20190508143648.8153-1-liwei391@huawei.com Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Zhipeng Xie <xiezhipeng1@huawei.com> Link: https://lkml.kernel.org/r/20190704194355.GI10740@kernel.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf/util/machine.c')
-rw-r--r--tools/perf/util/machine.c25
1 files changed, 23 insertions, 2 deletions
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index dc7aafe45a2b..e00dc413652d 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -209,6 +209,18 @@ void machine__exit(struct machine *machine)
for (i = 0; i < THREADS__TABLE_SIZE; i++) {
struct threads *threads = &machine->threads[i];
+ struct thread *thread, *n;
+ /*
+ * Forget about the dead, at this point whatever threads were
+ * left in the dead lists better have a reference count taken
+ * by who is using them, and then, when they drop those references
+ * and it finally hits zero, thread__put() will check and see that
+ * its not in the dead threads list and will not try to remove it
+ * from there, just calling thread__delete() straight away.
+ */
+ list_for_each_entry_safe(thread, n, &threads->dead, node)
+ list_del_init(&thread->node);
+
exit_rwsem(&threads->lock);
}
}
@@ -1758,9 +1770,11 @@ static void __machine__remove_thread(struct machine *machine, struct thread *th,
if (threads->last_match == th)
threads__set_last_match(threads, NULL);
- BUG_ON(refcount_read(&th->refcnt) == 0);
if (lock)
down_write(&threads->lock);
+
+ BUG_ON(refcount_read(&th->refcnt) == 0);
+
rb_erase_cached(&th->rb_node, &threads->entries);
RB_CLEAR_NODE(&th->rb_node);
--threads->nr;
@@ -1770,9 +1784,16 @@ static void __machine__remove_thread(struct machine *machine, struct thread *th,
* will be called and we will remove it from the dead_threads list.
*/
list_add_tail(&th->node, &threads->dead);
+
+ /*
+ * We need to do the put here because if this is the last refcount,
+ * then we will be touching the threads->dead head when removing the
+ * thread.
+ */
+ thread__put(th);
+
if (lock)
up_write(&threads->lock);
- thread__put(th);
}
void machine__remove_thread(struct machine *machine, struct thread *th)