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Subject[PATCH 1/6] mmput: use notifier chain to call subsystem exit handler.
Date
From: Jérôme Glisse <jglisse@redhat.com>

Several subsystem require a callback when a mm struct is being destroy
so that they can cleanup there respective per mm struct. Instead of
having each subsystem add its callback to mmput use a notifier chain
to call each of the subsystem.

This will allow new subsystem to register callback even if they are
module. There should be no contention on the rw semaphore protecting
the call chain and the impact on the code path should be low and
burried in the noise.

Note that this patch also move the call to cleanup functions after
exit_mmap so that new call back can assume that mmu_notifier_release
have already been call. This does not impact existing cleanup functions
as they do not rely on anything that exit_mmap is freeing. Also moved
khugepaged_exit to exit_mmap so that ordering is preserved for that
function.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
---
fs/aio.c | 29 ++++++++++++++++++++++-------
include/linux/aio.h | 2 --
include/linux/ksm.h | 11 -----------
include/linux/sched.h | 5 +++++
include/linux/uprobes.h | 1 -
kernel/events/uprobes.c | 19 ++++++++++++++++---
kernel/fork.c | 22 ++++++++++++++++++----
mm/ksm.c | 26 +++++++++++++++++++++-----
mm/mmap.c | 3 +++
9 files changed, 85 insertions(+), 33 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index c1d8c48..1d06e92 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -40,6 +40,7 @@
#include <linux/ramfs.h>
#include <linux/percpu-refcount.h>
#include <linux/mount.h>
+#include <linux/notifier.h>

#include <asm/kmap_types.h>
#include <asm/uaccess.h>
@@ -774,20 +775,22 @@ ssize_t wait_on_sync_kiocb(struct kiocb *req)
EXPORT_SYMBOL(wait_on_sync_kiocb);

/*
- * exit_aio: called when the last user of mm goes away. At this point, there is
+ * aio_exit: called when the last user of mm goes away. At this point, there is
* no way for any new requests to be submited or any of the io_* syscalls to be
* called on the context.
*
* There may be outstanding kiocbs, but free_ioctx() will explicitly wait on
* them.
*/
-void exit_aio(struct mm_struct *mm)
+static int aio_exit(struct notifier_block *nb,
+ unsigned long action, void *data)
{
+ struct mm_struct *mm = data;
struct kioctx_table *table = rcu_dereference_raw(mm->ioctx_table);
int i;

if (!table)
- return;
+ return 0;

for (i = 0; i < table->nr; ++i) {
struct kioctx *ctx = table->table[i];
@@ -796,10 +799,10 @@ void exit_aio(struct mm_struct *mm)
continue;
/*
* We don't need to bother with munmap() here - exit_mmap(mm)
- * is coming and it'll unmap everything. And we simply can't,
- * this is not necessarily our ->mm.
- * Since kill_ioctx() uses non-zero ->mmap_size as indicator
- * that it needs to unmap the area, just set it to 0.
+ * have already been call and everything is unmap by now. But
+ * to be safe set ->mmap_size to 0 since aio_free_ring() uses
+ * non-zero ->mmap_size as indicator that it needs to unmap the
+ * area.
*/
ctx->mmap_size = 0;
kill_ioctx(mm, ctx, NULL);
@@ -807,6 +810,7 @@ void exit_aio(struct mm_struct *mm)

RCU_INIT_POINTER(mm->ioctx_table, NULL);
kfree(table);
+ return 0;
}

static void put_reqs_available(struct kioctx *ctx, unsigned nr)
@@ -1629,3 +1633,14 @@ SYSCALL_DEFINE5(io_getevents, aio_context_t, ctx_id,
}
return ret;
}
+
+static struct notifier_block aio_mmput_nb = {
+ .notifier_call = aio_exit,
+ .priority = 1,
+};
+
+static int __init aio_init(void)
+{
+ return mmput_register_notifier(&aio_mmput_nb);
+}
+subsys_initcall(aio_init);
diff --git a/include/linux/aio.h b/include/linux/aio.h
index d9c92da..6308fac 100644
--- a/include/linux/aio.h
+++ b/include/linux/aio.h
@@ -73,7 +73,6 @@ static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
extern ssize_t wait_on_sync_kiocb(struct kiocb *iocb);
extern void aio_complete(struct kiocb *iocb, long res, long res2);
struct mm_struct;
-extern void exit_aio(struct mm_struct *mm);
extern long do_io_submit(aio_context_t ctx_id, long nr,
struct iocb __user *__user *iocbpp, bool compat);
void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel);
@@ -81,7 +80,6 @@ void kiocb_set_cancel_fn(struct kiocb *req, kiocb_cancel_fn *cancel);
static inline ssize_t wait_on_sync_kiocb(struct kiocb *iocb) { return 0; }
static inline void aio_complete(struct kiocb *iocb, long res, long res2) { }
struct mm_struct;
-static inline void exit_aio(struct mm_struct *mm) { }
static inline long do_io_submit(aio_context_t ctx_id, long nr,
struct iocb __user * __user *iocbpp,
bool compat) { return 0; }
diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index 3be6bb1..84c184f 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -20,7 +20,6 @@ struct mem_cgroup;
int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
unsigned long end, int advice, unsigned long *vm_flags);
int __ksm_enter(struct mm_struct *mm);
-void __ksm_exit(struct mm_struct *mm);

static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
{
@@ -29,12 +28,6 @@ static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
return 0;
}

-static inline void ksm_exit(struct mm_struct *mm)
-{
- if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
- __ksm_exit(mm);
-}
-
/*
* A KSM page is one of those write-protected "shared pages" or "merged pages"
* which KSM maps into multiple mms, wherever identical anonymous page content
@@ -83,10 +76,6 @@ static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm)
return 0;
}

-static inline void ksm_exit(struct mm_struct *mm)
-{
-}
-
static inline int PageKsm(struct page *page)
{
return 0;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 322d4fc..428b3cf 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2384,6 +2384,11 @@ static inline void mmdrop(struct mm_struct * mm)
__mmdrop(mm);
}

+/* mmput call list of notifier and subsystem/module can register
+ * new one through this call.
+ */
+extern int mmput_register_notifier(struct notifier_block *nb);
+extern int mmput_unregister_notifier(struct notifier_block *nb);
/* mmput gets rid of the mappings and all user-space */
extern void mmput(struct mm_struct *);
/* Grab a reference to a task's mm, if it is not already going away */
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 4f844c6..44e7267 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -120,7 +120,6 @@ extern int uprobe_pre_sstep_notifier(struct pt_regs *regs);
extern void uprobe_notify_resume(struct pt_regs *regs);
extern bool uprobe_deny_signal(void);
extern bool arch_uprobe_skip_sstep(struct arch_uprobe *aup, struct pt_regs *regs);
-extern void uprobe_clear_state(struct mm_struct *mm);
extern int arch_uprobe_analyze_insn(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long addr);
extern int arch_uprobe_pre_xol(struct arch_uprobe *aup, struct pt_regs *regs);
extern int arch_uprobe_post_xol(struct arch_uprobe *aup, struct pt_regs *regs);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 46b7c31..32b04dc 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -37,6 +37,7 @@
#include <linux/percpu-rwsem.h>
#include <linux/task_work.h>
#include <linux/shmem_fs.h>
+#include <linux/notifier.h>

#include <linux/uprobes.h>

@@ -1220,16 +1221,19 @@ static struct xol_area *get_xol_area(void)
/*
* uprobe_clear_state - Free the area allocated for slots.
*/
-void uprobe_clear_state(struct mm_struct *mm)
+static int uprobe_clear_state(struct notifier_block *nb,
+ unsigned long action, void *data)
{
+ struct mm_struct *mm = data;
struct xol_area *area = mm->uprobes_state.xol_area;

if (!area)
- return;
+ return 0;

put_page(area->page);
kfree(area->bitmap);
kfree(area);
+ return 0;
}

void uprobe_start_dup_mmap(void)
@@ -1979,9 +1983,14 @@ static struct notifier_block uprobe_exception_nb = {
.priority = INT_MAX-1, /* notified after kprobes, kgdb */
};

+static struct notifier_block uprobe_mmput_nb = {
+ .notifier_call = uprobe_clear_state,
+ .priority = 0,
+};
+
static int __init init_uprobes(void)
{
- int i;
+ int i, err;

for (i = 0; i < UPROBES_HASH_SZ; i++)
mutex_init(&uprobes_mmap_mutex[i]);
@@ -1989,6 +1998,10 @@ static int __init init_uprobes(void)
if (percpu_init_rwsem(&dup_mmap_sem))
return -ENOMEM;

+ err = mmput_register_notifier(&uprobe_mmput_nb);
+ if (err)
+ return err;
+
return register_die_notifier(&uprobe_exception_nb);
}
__initcall(init_uprobes);
diff --git a/kernel/fork.c b/kernel/fork.c
index dd8864f..b448509 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -87,6 +87,8 @@
#define CREATE_TRACE_POINTS
#include <trace/events/task.h>

+static BLOCKING_NOTIFIER_HEAD(mmput_notifier);
+
/*
* Protected counters by write_lock_irq(&tasklist_lock)
*/
@@ -623,6 +625,21 @@ void __mmdrop(struct mm_struct *mm)
EXPORT_SYMBOL_GPL(__mmdrop);

/*
+ * Register a notifier that will be call by mmput
+ */
+int mmput_register_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_register(&mmput_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(mmput_register_notifier);
+
+int mmput_unregister_notifier(struct notifier_block *nb)
+{
+ return blocking_notifier_chain_unregister(&mmput_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(mmput_unregister_notifier);
+
+/*
* Decrement the use count and release all resources for an mm.
*/
void mmput(struct mm_struct *mm)
@@ -630,11 +647,8 @@ void mmput(struct mm_struct *mm)
might_sleep();

if (atomic_dec_and_test(&mm->mm_users)) {
- uprobe_clear_state(mm);
- exit_aio(mm);
- ksm_exit(mm);
- khugepaged_exit(mm); /* must run before exit_mmap */
exit_mmap(mm);
+ blocking_notifier_call_chain(&mmput_notifier, 0, mm);
set_mm_exe_file(mm, NULL);
if (!list_empty(&mm->mmlist)) {
spin_lock(&mmlist_lock);
diff --git a/mm/ksm.c b/mm/ksm.c
index 346ddc9..cb1e976 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -37,6 +37,7 @@
#include <linux/freezer.h>
#include <linux/oom.h>
#include <linux/numa.h>
+#include <linux/notifier.h>

#include <asm/tlbflush.h>
#include "internal.h"
@@ -1586,7 +1587,7 @@ static struct rmap_item *scan_get_next_rmap_item(struct page **page)
ksm_scan.mm_slot = slot;
spin_unlock(&ksm_mmlist_lock);
/*
- * Although we tested list_empty() above, a racing __ksm_exit
+ * Although we tested list_empty() above, a racing ksm_exit
* of the last mm on the list may have removed it since then.
*/
if (slot == &ksm_mm_head)
@@ -1658,9 +1659,9 @@ next_mm:
/*
* We've completed a full scan of all vmas, holding mmap_sem
* throughout, and found no VM_MERGEABLE: so do the same as
- * __ksm_exit does to remove this mm from all our lists now.
- * This applies either when cleaning up after __ksm_exit
- * (but beware: we can reach here even before __ksm_exit),
+ * ksm_exit does to remove this mm from all our lists now.
+ * This applies either when cleaning up after ksm_exit
+ * (but beware: we can reach here even before ksm_exit),
* or when all VM_MERGEABLE areas have been unmapped (and
* mmap_sem then protects against race with MADV_MERGEABLE).
*/
@@ -1821,11 +1822,16 @@ int __ksm_enter(struct mm_struct *mm)
return 0;
}

-void __ksm_exit(struct mm_struct *mm)
+static int ksm_exit(struct notifier_block *nb,
+ unsigned long action, void *data)
{
+ struct mm_struct *mm = data;
struct mm_slot *mm_slot;
int easy_to_free = 0;

+ if (!test_bit(MMF_VM_MERGEABLE, &mm->flags))
+ return 0;
+
/*
* This process is exiting: if it's straightforward (as is the
* case when ksmd was never running), free mm_slot immediately.
@@ -1857,6 +1863,7 @@ void __ksm_exit(struct mm_struct *mm)
down_write(&mm->mmap_sem);
up_write(&mm->mmap_sem);
}
+ return 0;
}

struct page *ksm_might_need_to_copy(struct page *page,
@@ -2305,11 +2312,20 @@ static struct attribute_group ksm_attr_group = {
};
#endif /* CONFIG_SYSFS */

+static struct notifier_block ksm_mmput_nb = {
+ .notifier_call = ksm_exit,
+ .priority = 2,
+};
+
static int __init ksm_init(void)
{
struct task_struct *ksm_thread;
int err;

+ err = mmput_register_notifier(&ksm_mmput_nb);
+ if (err)
+ return err;
+
err = ksm_slab_init();
if (err)
goto out;
diff --git a/mm/mmap.c b/mm/mmap.c
index 61aec93..b684a21 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2775,6 +2775,9 @@ void exit_mmap(struct mm_struct *mm)
struct vm_area_struct *vma;
unsigned long nr_accounted = 0;

+ /* Important to call this first. */
+ khugepaged_exit(mm);
+
/* mm's last user has gone, and its about to be pulled down */
mmu_notifier_release(mm);

--
1.9.0
--
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