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    Subject[PATCH 4/4] coredump: shift down_write(mmap_sem) into coredump_wait()
    - move the cprm.mm_flags checks up, before we take mmap_sem

    - move down_write(mmap_sem) and ->core_state check from do_coredump()
    to coredump_wait()

    This simplifies the code and makes the locking symmetrical.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    ---

    fs/exec.c | 19 +++++++------------
    1 file changed, 7 insertions(+), 12 deletions(-)

    --- 34-rc1/fs/exec.c~4_MMAP_SEM 2010-03-16 19:09:50.000000000 +0100
    +++ 34-rc1/fs/exec.c 2010-03-16 19:28:23.000000000 +0100
    @@ -1659,12 +1659,15 @@ static int coredump_wait(int exit_code,
    struct task_struct *tsk = current;
    struct mm_struct *mm = tsk->mm;
    struct completion *vfork_done;
    - int core_waiters;
    + int core_waiters = -EBUSY;

    init_completion(&core_state->startup);
    core_state->dumper.task = tsk;
    core_state->dumper.next = NULL;
    - core_waiters = zap_threads(tsk, mm, core_state, exit_code);
    +
    + down_write(&mm->mmap_sem);
    + if (!mm->core_state)
    + core_waiters = zap_threads(tsk, mm, core_state, exit_code);
    up_write(&mm->mmap_sem);

    if (unlikely(core_waiters < 0))
    @@ -1857,20 +1860,12 @@ void do_coredump(long signr, int exit_co
    binfmt = mm->binfmt;
    if (!binfmt || !binfmt->core_dump)
    goto fail;
    + if (!__get_dumpable(cprm.mm_flags))
    + goto fail;

    cred = prepare_creds();
    if (!cred)
    goto fail;
    -
    - down_write(&mm->mmap_sem);
    - /*
    - * If another thread got here first, or we are not dumpable, bail out.
    - */
    - if (mm->core_state || !__get_dumpable(cprm.mm_flags)) {
    - up_write(&mm->mmap_sem);
    - goto fail_creds;
    - }
    -
    /*
    * We cannot trust fsuid as being the "true" uid of the
    * process nor do we know its entire history. We only know it


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