Commit 246bb0b1 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

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: default avatarOleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7b34e428

fs/aio.c

+0 −2
Original line number Diff line number Diff line
@@ -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 *mm) 
	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);

include/linux/sched.h

+1 −2
Original line number 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_EXITPIDONE	0x00000008	/* pi exit done on shut down */

#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_SUPERPRIV	0x00000100	/* used super-user privileges */

#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_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 */

kernel/fork.c

+2 −2
Original line number Diff line number Diff line
@@ -474,7 +474,7 @@ 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()
@@ -487,7 +487,7 @@ struct mm_struct *get_task_mm(struct task_struct *task) 
	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);

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