Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754821AbYFAP3x (ORCPT ); Sun, 1 Jun 2008 11:29:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752561AbYFAP3Q (ORCPT ); Sun, 1 Jun 2008 11:29:16 -0400 Received: from x346.tv-sign.ru ([89.108.83.215]:58894 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752374AbYFAP3O (ORCPT ); Sun, 1 Jun 2008 11:29:14 -0400 Date: Sun, 1 Jun 2008 19:30:44 +0400 From: Oleg Nesterov To: Andrew Morton Cc: "Eric W. Biederman" , Ingo Molnar , Linus Torvalds , Roland McGrath , linux-kernel@vger.kernel.org Subject: [PATCH 2/3] kill PF_BORROWED_MM in favour of PF_KTHREAD Message-ID: <20080601153044.GA8241@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4191 Lines: 103 Kill PF_BORROWED_MM. Change use_mm/unuse_mm to not play with ->flags, and do s/PF_BORROWED_MM/PF_KTHREAD/ for a couple of other users. No functional changes yet. But this allows us to do further fixes/cleanups. oom_kill/ptrace/etc often check "p->mm != NULL" to filter out the kthreads, this is wrong because of use_mm(). The problem with PF_BORROWED_MM is that we need task_lock() to avoid races. With this patch we can check PF_KTHREAD directly, or use a simple lockless helper: /* The result must not be dereferenced !!! */ struct mm_struct *__get_task_mm(struct task_struct *tsk) { if (tsk->flags & PF_KTHREAD) return NULL; return tsk->mm; } Note also ecard_task(). It runs with ->mm != NULL, but it's the kernel thread without PF_BORROWED_MM. Signed-off-by: Oleg Nesterov include/linux/sched.h | 3 +-- fs/aio.c | 2 -- kernel/fork.c | 4 ++-- kernel/power/process.c | 2 +- 4 files changed, 4 insertions(+), 7 deletions(-) --- 26-rc2/include/linux/sched.h~3_USE_PF_KTHREAD 2008-05-18 15:44:16.000000000 +0400 +++ 26-rc2/include/linux/sched.h 2008-05-18 19:11:44.000000000 +0400 @@ -1500,7 +1500,7 @@ static inline void put_task_struct(struc #define PF_KSWAPD 0x00040000 /* I am kswapd */ #define PF_SWAPOFF 0x00080000 /* I am in swapoff */ #define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */ -#define PF_BORROWED_MM 0x00200000 /* I am a kthread doing use_mm */ +#define PF_KTHREAD 0x00200000 /* I am a kernel thread */ #define PF_RANDOMIZE 0x00400000 /* randomize virtual address space */ #define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */ #define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */ @@ -1508,7 +1508,6 @@ static inline void put_task_struct(struc #define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */ #define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */ #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */ -#define PF_KTHREAD 0x80000000 /* I am a kernel thread */ /* * Only the _current_ task can read/write to tsk->flags, but other --- 26-rc2/fs/aio.c~3_USE_PF_KTHREAD 2008-05-18 17:20:42.000000000 +0400 +++ 26-rc2/fs/aio.c 2008-05-18 19:19:07.000000000 +0400 @@ -586,7 +586,6 @@ static void use_mm(struct mm_struct *mm) struct task_struct *tsk = current; task_lock(tsk); - tsk->flags |= PF_BORROWED_MM; active_mm = tsk->active_mm; atomic_inc(&mm->mm_count); tsk->mm = mm; @@ -610,7 +609,6 @@ static void unuse_mm(struct mm_struct *m struct task_struct *tsk = current; task_lock(tsk); - tsk->flags &= ~PF_BORROWED_MM; tsk->mm = NULL; /* active_mm is still 'mm' */ enter_lazy_tlb(mm, tsk); --- 26-rc2/kernel/fork.c~3_USE_PF_KTHREAD 2008-05-18 15:44:18.000000000 +0400 +++ 26-rc2/kernel/fork.c 2008-05-18 19:21:02.000000000 +0400 @@ -447,7 +447,7 @@ EXPORT_SYMBOL_GPL(mmput); /** * get_task_mm - acquire a reference to the task's mm * - * Returns %NULL if the task has no mm. Checks PF_BORROWED_MM (meaning + * Returns %NULL if the task has no mm. Checks PF_KTHREAD (meaning * this kernel workthread has transiently adopted a user mm with use_mm, * to do its AIO) is not set and if so returns a reference to it, after * bumping up the use count. User must release the mm via mmput() @@ -460,7 +460,7 @@ struct mm_struct *get_task_mm(struct tas task_lock(task); mm = task->mm; if (mm) { - if (task->flags & PF_BORROWED_MM) + if (task->flags & PF_KTHREAD) mm = NULL; else atomic_inc(&mm->mm_users); --- 26-rc2/kernel/power/process.c~3_USE_PF_KTHREAD 2008-05-18 15:42:44.000000000 +0400 +++ 26-rc2/kernel/power/process.c 2008-05-18 19:22:40.000000000 +0400 @@ -86,7 +86,7 @@ static void fake_signal_wake_up(struct t static int has_mm(struct task_struct *p) { - return (p->mm && !(p->flags & PF_BORROWED_MM)); + return (p->mm && !(p->flags & PF_KTHREAD)); } /** -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/