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    Subject[tip:perf/core] perf: Fix perf_event_comm() vs. exec() assumption
    Commit-ID:  e041e328c4b41e1db79bfe5ba9992c2ed771ad19
    Gitweb: http://git.kernel.org/tip/e041e328c4b41e1db79bfe5ba9992c2ed771ad19
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Wed, 21 May 2014 17:32:19 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Fri, 6 Jun 2014 07:54:02 +0200

    perf: Fix perf_event_comm() vs. exec() assumption

    perf_event_comm() assumes that set_task_comm() is only called on
    exec(), and in particular that its only called on current.

    Neither are true, as Dave reported a WARN triggered by set_task_comm()
    being called on !current.

    Separate the exec() hook from the comm hook.

    Reported-by: Dave Jones <davej@redhat.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: linux-fsdevel@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Link: http://lkml.kernel.org/r/20140521153219.GH5226@laptop.programming.kicks-ass.net
    [ Build fix. ]
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    fs/exec.c | 1 +
    include/linux/perf_event.h | 4 +++-
    kernel/events/core.c | 28 ++++++++++++++++------------
    3 files changed, 20 insertions(+), 13 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index 238b7aa..a038a41 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -1110,6 +1110,7 @@ void setup_new_exec(struct linux_binprm * bprm)
    else
    set_dumpable(current->mm, suid_dumpable);

    + perf_event_exec();
    set_task_comm(current, kbasename(bprm->filename));

    /* Set the new mm task size. We have to do that late because it may
    diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    index 3ef6ea1..9b5cd19 100644
    --- a/include/linux/perf_event.h
    +++ b/include/linux/perf_event.h
    @@ -695,6 +695,7 @@ extern struct perf_guest_info_callbacks *perf_guest_cbs;
    extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
    extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);

    +extern void perf_event_exec(void);
    extern void perf_event_comm(struct task_struct *tsk);
    extern void perf_event_fork(struct task_struct *tsk);

    @@ -772,7 +773,7 @@ extern void perf_event_enable(struct perf_event *event);
    extern void perf_event_disable(struct perf_event *event);
    extern int __perf_event_disable(void *info);
    extern void perf_event_task_tick(void);
    -#else
    +#else /* !CONFIG_PERF_EVENTS: */
    static inline void
    perf_event_task_sched_in(struct task_struct *prev,
    struct task_struct *task) { }
    @@ -802,6 +803,7 @@ static inline int perf_unregister_guest_info_callbacks
    (struct perf_guest_info_callbacks *callbacks) { return 0; }

    static inline void perf_event_mmap(struct vm_area_struct *vma) { }
    +static inline void perf_event_exec(void) { }
    static inline void perf_event_comm(struct task_struct *tsk) { }
    static inline void perf_event_fork(struct task_struct *tsk) { }
    static inline void perf_event_init(void) { }
    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 440eefc..647698f 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -2970,6 +2970,22 @@ out:
    local_irq_restore(flags);
    }

    +void perf_event_exec(void)
    +{
    + struct perf_event_context *ctx;
    + int ctxn;
    +
    + rcu_read_lock();
    + for_each_task_context_nr(ctxn) {
    + ctx = current->perf_event_ctxp[ctxn];
    + if (!ctx)
    + continue;
    +
    + perf_event_enable_on_exec(ctx);
    + }
    + rcu_read_unlock();
    +}
    +
    /*
    * Cross CPU call to read the hardware event
    */
    @@ -5057,18 +5073,6 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
    void perf_event_comm(struct task_struct *task)
    {
    struct perf_comm_event comm_event;
    - struct perf_event_context *ctx;
    - int ctxn;
    -
    - rcu_read_lock();
    - for_each_task_context_nr(ctxn) {
    - ctx = task->perf_event_ctxp[ctxn];
    - if (!ctx)
    - continue;
    -
    - perf_event_enable_on_exec(ctx);
    - }
    - rcu_read_unlock();

    if (!atomic_read(&nr_comm_events))
    return;

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