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Tsirkin" , Jason Wang Cc: guomin chen , , , , Subject: [PATCH] Fix mm->owner point to a task that does not exists. Date: Wed, 12 Dec 2018 09:54:02 +0800 Message-Id: <1544579642-29626-1-git-send-email-gchen.guomin@gmail.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: guomin chen Under normal circumstances,When do_exit exits, mm->owner will be updated on exit_mm(). but when the kernel process calls unuse_mm() and then exits,mm->owner cannot be updated. And it will point to a task that has been released. Below is my issue on vhost_net: A, B are two kernel processes(such as vhost_worker), C is a user space process(such as qemu), and all three use the mm of the user process C. Now, because user process C exits abnormally, the owner of this mm becomes A. When A calls unuse_mm and exits, this mm->ower still points to the A that has been released. When B accesses this mm->owner again, A has been released. Process A Process B vhost_worker() vhost_worker() --------- --------- use_mm() use_mm() ... unuse_mm() tsk->mm=NULL do_exit() page fault exit_mm() access mm->owner can't update owner kernel Oops unuse_mm() Cc: "Michael S. Tsirkin" Cc: Jason Wang Cc: Cc: Cc: Cc: Signed-off-by: guomin chen --- drivers/vhost/vhost.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 6b98d8e..7f8586a 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -368,6 +368,10 @@ static int vhost_worker(void *data) } } unuse_mm(dev->mm); + /* current->mm needs to be processed by the later exit_mm() */ + task_lock(current); + current->mm = dev->mm; + task_unlock(current); set_fs(oldfs); return 0; } -- 1.8.3.1