Oleg found that there is a potential race if we don't flush the task for threads (VM_CLONE):
"Suppose we have a task T1 which has the valid vmacache, T1->vmacache_seqnum == T1->mm->vmacache_seqnum == 0. Suppose it sleeps a lot. Suppose that its subthread T2 does a lot munmap's, finally mm->vmacache_seqnum becomes zero again and T2 calls vmacache_flush_all(). T1 wakes up and does clone(CLONE_VM). The new thread T3 gets the copy of T2's ->vmacache_seqnum and ->vmacache[]. T2 continues, vmacache_flush_all() finds T1 and does vmacache_flush(T1). But the new thread T3 is not on the list yet, vmacache_flush_all() can't find it. So T3 will run with vmacache_valid() == T (till the next invalidate(mm) of course) but its ->vmacache[] points to nowhere." Address this by moving the flush call into copy_mm(), instead of only having it in dup_mm(). Signed-off-by: Davidlohr Bueso <davidl...@hp.com> --- kernel/fork.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 3e02737..45b6241 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -841,9 +841,6 @@ static struct mm_struct *dup_mm(struct task_struct *tsk) if (mm->binfmt && !try_module_get(mm->binfmt->module)) goto free_pt; - /* initialize the new vmacache entries */ - vmacache_flush(tsk); - return mm; free_pt: @@ -887,6 +884,9 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk) if (!oldmm) return 0; + /* initialize the new vmacache entries */ + vmacache_flush(tsk); + if (clone_flags & CLONE_VM) { atomic_inc(&oldmm->mm_users); mm = oldmm; -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/