Merge tag 'perf-urgent-for-mingo-5.3-20190708-2' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core

Pull perf/urgent fixes from Arnaldo Carvalho de Melo:

core:

  Arnaldo Carvalho de Melo:

  - Allow references to thread objects after__machine_exit(), fixing a bug with
    'perf sched lat' where that happens, i.e. after perf_session__delete() we
    still have references to threads that were in a linked list whose head was
    freed in perf_session__delete(), causing a segfault, fix it.

  Jiri Olsa:

  - Do not rely on errno values for precise_ip fallback, fixing the default
    use case for 'perf record' on some AMD servers, when no events are specified
    and we try to use "cycles:P", i.e. with the maximum precision level.

BPF:

  Song Liu:

  - Assign proper ff->ph in perf_event__synthesize_features(), fixing a bug
    when using pipe mode, i.e.  'perf record -o -'.

tools headers:

  Arnaldo Carvalho de Melo:

  - Sync kvm headers with the kernel sources

perf tests:

  Seeteena Thoufeek:

  - Fix record+probe_libc_inet_pton.sh for powerpc64, where without the
    debuginfo package for the 'ping' utility we can't resolve its symbols,
    so admit getting "[unknown]" for that backtrace line.

perf python:

  Arnaldo Carvalho de Melo:

  - Remove -fstack-protector-strong if clang doesn't have it, fixing the build
    with clang on fedora:30, oracleline:7, centos:7.

perf jvmti:

  Jiri Olsa:

  - Address gcc string overflow warning for strncpy()

build:

  Arnaldo Carvalho de Melo:

  - Check if gettid() is available before providing helper, as recent
    versions of glibc started to provide gettid().

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 20 insertions, 3 deletions

diff --git a/tools/perf/util/thread.c b/tools/perf/util/thread.c
index aab7807d445f..3e29a4e8b5e6 100644
--- a/tools/perf/util/thread.c
+++ b/tools/perf/util/thread.c
@@ -125,10 +125,27 @@ void thread__put(struct thread *thread)
 {
 	if (thread && refcount_dec_and_test(&thread->refcnt)) {
 		/*
-		 * Remove it from the dead_threads list, as last reference
-		 * is gone.
+		 * Remove it from the dead threads list, as last reference is
+		 * gone, if it is in a dead threads list.
+		 *
+		 * We may not be there anymore if say, the machine where it was
+		 * stored was already deleted, so we already removed it from
+		 * the dead threads and some other piece of code still keeps a
+		 * reference.
+		 *
+		 * This is what 'perf sched' does and finally drops it in
+		 * perf_sched__lat(), where it calls perf_sched__read_events(),
+		 * that processes the events by creating a session and deleting
+		 * it, which ends up destroying the list heads for the dead
+		 * threads, but before it does that it removes all threads from
+		 * it using list_del_init().
+		 *
+		 * So we need to check here if it is in a dead threads list and
+		 * if so, remove it before finally deleting the thread, to avoid
+		 * an use after free situation.
 		 */
-		list_del_init(&thread->node);
+		if (!list_empty(&thread->node))
+			list_del_init(&thread->node);
 		thread__delete(thread);
 	}
 }