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    Subject[tip:perf/urgent] perf: Fix perf_event_init_task()/perf_event_free_task() interaction
    Commit-ID:  8550d7cb6ed6c89add49c3b6ad4c753ab8a3d7f9
    Gitweb: http://git.kernel.org/tip/8550d7cb6ed6c89add49c3b6ad4c753ab8a3d7f9
    Author: Oleg Nesterov <oleg@redhat.com>
    AuthorDate: Wed, 19 Jan 2011 19:22:28 +0100
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 19 Jan 2011 20:04:28 +0100

    perf: Fix perf_event_init_task()/perf_event_free_task() interaction

    perf_event_init_task() should clear child->perf_event_ctxp[]
    before anything else. Otherwise, if
    perf_event_init_context(perf_hw_context) fails,
    perf_event_free_task() can free perf_event_ctxp[perf_sw_context]
    copied from parent->perf_event_ctxp[] by dup_task_struct().

    Also move the initialization of perf_event_mutex and
    perf_event_list from perf_event_init_context() to
    perf_event_init_context().

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Alan Stern <stern@rowland.harvard.edu>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Prasad <prasad@linux.vnet.ibm.com>
    Cc: Roland McGrath <roland@redhat.com>
    LKML-Reference: <20110119182228.GC12183@redhat.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/perf_event.c | 9 ++++-----
    1 files changed, 4 insertions(+), 5 deletions(-)

    diff --git a/kernel/perf_event.c b/kernel/perf_event.c
    index 4ec55ef..244ca3a 100644
    --- a/kernel/perf_event.c
    +++ b/kernel/perf_event.c
    @@ -6446,11 +6446,6 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
    unsigned long flags;
    int ret = 0;

    - child->perf_event_ctxp[ctxn] = NULL;
    -
    - mutex_init(&child->perf_event_mutex);
    - INIT_LIST_HEAD(&child->perf_event_list);
    -
    if (likely(!parent->perf_event_ctxp[ctxn]))
    return 0;

    @@ -6539,6 +6534,10 @@ int perf_event_init_task(struct task_struct *child)
    {
    int ctxn, ret;

    + memset(child->perf_event_ctxp, 0, sizeof(child->perf_event_ctxp));
    + mutex_init(&child->perf_event_mutex);
    + INIT_LIST_HEAD(&child->perf_event_list);
    +
    for_each_task_context_nr(ctxn) {
    ret = perf_event_init_context(child, ctxn);
    if (ret)

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