The patch titled
kill PF_BORROWED_MM in favour of PF_KTHREAD
has been added to the -mm tree. Its filename is
kill-pf_borrowed_mm-in-favour-of-pf_kthread.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: kill PF_BORROWED_MM in favour of PF_KTHREAD
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/aio.c | 2 --
include/linux/sched.h | 3 +--
kernel/fork.c | 4 ++--
kernel/power/process.c | 2 +-
4 files changed, 4 insertions(+), 7 deletions(-)
diff -puN fs/aio.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread fs/aio.c
--- a/fs/aio.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread
+++ a/fs/aio.c
@@ -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;
@@ -614,7 +613,6 @@ 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);
diff -puN include/linux/sched.h~kill-pf_borrowed_mm-in-favour-of-pf_kthread include/linux/sched.h
--- a/include/linux/sched.h~kill-pf_borrowed_mm-in-favour-of-pf_kthread
+++ a/include/linux/sched.h
@@ -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
diff -puN kernel/fork.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread kernel/fork.c
--- a/kernel/fork.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread
+++ a/kernel/fork.c
@@ -452,7 +452,7 @@ 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()
@@ -465,7 +465,7 @@ 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);
diff -puN kernel/power/process.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread kernel/power/process.c
--- a/kernel/power/process.c~kill-pf_borrowed_mm-in-favour-of-pf_kthread
+++ a/kernel/power/process.c
@@ -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));
}
/**
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
vt-fix-vc_resize-locking.patch
introduce-pf_kthread-flag.patch
kill-pf_borrowed_mm-in-favour-of-pf_kthread.patch
coredump-zap_threads-must-skip-kernel-threads.patch
uml-activate_mm-remove-the-dead-pf_borrowed_mm-check.patch
posix-timers-timer_delete-remove-the-bogus-it_process-=-null-check.patch
posix-timers-release_posix_timer-kill-the-bogus-put_task_struct-it_process.patch
signals-collect_signal-remove-the-unneeded-sigismember-check.patch
signals-collect_signal-simplify-the-still_pending-logic.patch
signals-change-collect_signal-to-return-void.patch
__exit_signal-dont-take-rcu-lock.patch
signals-dequeue_signal-dont-check-signal_group_exit-when-setting-signal_stop_dequeued.patch
signals-do_signal_stop-kill-the-signal_unkillable-check.patch
coredump-zap_threads-comments-use-while_each_thread.patch
distinct-tgid-tid-i-o-statistics.patch
--
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