perf: fix perf bug in fork()
Peter Zijlstra [Thu, 2 Oct 2014 23:17:02 +0000 (16:17 -0700)]
commit 6c72e3501d0d62fc064d3680e5234f3463ec5a86 upstream.

Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by
calling perf_event_free_task() when failing sched_fork() we will not yet
have done the memset() on ->perf_event_ctxp[] and will therefore try and
'free' the inherited contexts, which are still in use by the parent
process.  This is bad..

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Sylvain 'ythier' Hitier <sylvain.hitier@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/events/core.c
kernel/fork.c

index 6bf387a..0b47334 100644 (file)
@@ -7482,8 +7482,10 @@ int perf_event_init_task(struct task_struct *child)
 
        for_each_task_context_nr(ctxn) {
                ret = perf_event_init_context(child, ctxn);
-               if (ret)
+               if (ret) {
+                       perf_event_free_task(child);
                        return ret;
+               }
        }
 
        return 0;
index 2c76e11..514dbc4 100644 (file)
@@ -1324,7 +1324,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
                goto bad_fork_cleanup_policy;
        retval = audit_alloc(p);
        if (retval)
-               goto bad_fork_cleanup_policy;
+               goto bad_fork_cleanup_perf;
        /* copy all the process information */
        retval = copy_semundo(clone_flags, p);
        if (retval)
@@ -1522,8 +1522,9 @@ bad_fork_cleanup_semundo:
        exit_sem(p);
 bad_fork_cleanup_audit:
        audit_free(p);
-bad_fork_cleanup_policy:
+bad_fork_cleanup_perf:
        perf_event_free_task(p);
+bad_fork_cleanup_policy:
 #ifdef CONFIG_NUMA
        mpol_put(p->mempolicy);
 bad_fork_cleanup_cgroup: