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From: Oleg Nesterov on 16 Mar 2010 15:50
- 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(a)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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