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Commit 246bb0b1 authored Jul 25, 2008 by Oleg Nesterov Committed by Linus Torvalds Jul 25, 2008

kill PF_BORROWED_MM in favour of PF_KTHREAD



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 <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7b34e428

fs/aio.c

+0 −2

Original line number	Original line	Diff line number	Diff line
	@@ -586,7 +586,6 @@ static void use_mm(struct mm_struct *mm)
	struct task_struct *tsk = current;		struct task_struct *tsk = current;

	task_lock(tsk);		task_lock(tsk);
	tsk->flags \|= PF_BORROWED_MM;
	active_mm = tsk->active_mm;		active_mm = tsk->active_mm;
	atomic_inc(&mm->mm_count);		atomic_inc(&mm->mm_count);
	tsk->mm = mm;		tsk->mm = mm;
	@@ -610,7 +609,6 @@ static void unuse_mm(struct mm_struct *mm)
	struct task_struct *tsk = current;		struct task_struct *tsk = current;

	task_lock(tsk);		task_lock(tsk);
	tsk->flags &= ~PF_BORROWED_MM;
	tsk->mm = NULL;		tsk->mm = NULL;
	/* active_mm is still 'mm' */		/* active_mm is still 'mm' */
	enter_lazy_tlb(mm, tsk);		enter_lazy_tlb(mm, tsk);

include/linux/sched.h

+1 −2

Original line number	Original line	Diff line number	Diff line
	@@ -1483,7 +1483,6 @@ static inline void put_task_struct(struct task_struct *t)
	#define PF_EXITING 0x00000004 /* getting shut down */		#define PF_EXITING 0x00000004 /* getting shut down */
	#define PF_EXITPIDONE 0x00000008 /* pi exit done on shut down */		#define PF_EXITPIDONE 0x00000008 /* pi exit done on shut down */
	#define PF_VCPU 0x00000010 /* I'm a virtual CPU */		#define PF_VCPU 0x00000010 /* I'm a virtual CPU */
	#define PF_KTHREAD 0x00000020 /* I am a kernel thread */
	#define PF_FORKNOEXEC 0x00000040 /* forked but didn't exec */		#define PF_FORKNOEXEC 0x00000040 /* forked but didn't exec */
	#define PF_SUPERPRIV 0x00000100 /* used super-user privileges */		#define PF_SUPERPRIV 0x00000100 /* used super-user privileges */
	#define PF_DUMPCORE 0x00000200 /* dumped core */		#define PF_DUMPCORE 0x00000200 /* dumped core */
	@@ -1497,7 +1496,7 @@ static inline void put_task_struct(struct task_struct *t)
	#define PF_KSWAPD 0x00040000 /* I am kswapd */		#define PF_KSWAPD 0x00040000 /* I am kswapd */
	#define PF_SWAPOFF 0x00080000 /* I am in swapoff */		#define PF_SWAPOFF 0x00080000 /* I am in swapoff */
	#define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory */		#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_RANDOMIZE 0x00400000 /* randomize virtual address space */
	#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */		#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
	#define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */		#define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */

kernel/fork.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -474,7 +474,7 @@ EXPORT_SYMBOL_GPL(mmput);
	/**		/**
	* get_task_mm - acquire a reference to the task's mm		* 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,		* 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		* 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()		* bumping up the use count. User must release the mm via mmput()
	@@ -487,7 +487,7 @@ struct mm_struct get_task_mm(struct task_struct task)
	task_lock(task);		task_lock(task);
	mm = task->mm;		mm = task->mm;
	if (mm) {		if (mm) {
	if (task->flags & PF_BORROWED_MM)		if (task->flags & PF_KTHREAD)
	mm = NULL;		mm = NULL;
	else		else
	atomic_inc(&mm->mm_users);		atomic_inc(&mm->mm_users);