The patch titled
ignore sigkill in get_user_pages during munlock
has been added to the -mm tree. Its filename is
mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock.patch
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------------------------------------------------------
Subject: ignore sigkill in get_user_pages during munlock
From: Lee Schermerhorn <Lee.Schermerhorn@xxxxxx>
An unfortunate side effect of "make-get_user_pages-interruptible" is that
it prevents a SIGKILL'd task from munlock-ing pages that it had mlocked,
resulting in freeing of mlocked pages. Freeing of mlocked pages, in
itself, is not so bad. We just count them now--altho' I had hoped to
remove this stat and add PG_MLOCKED to the free pages flags check.
However, consider pages in shared libraries mapped by more than one task
that a task mlocked--e.g., via mlockall(). If the task that mlocked the
pages exits via SIGKILL, these pages would be left mlocked and
unevictable.
Proposed fix:
Add another GUP flag to ignore sigkill when calling get_user_pages from
munlock()--similar to Kosaki Motohiro's 'IGNORE_VMA_PERMISSIONS flag for
the same purpose. We are not actually allocating memory in this case,
which "make-get_user_pages-interruptible" intends to avoid. We're just
munlocking pages that are already resident and mapped, and we're reusing
get_user_pages() to access those pages.
?? Maybe we should combine 'IGNORE_VMA_PERMISSIONS and '_IGNORE_SIGKILL
into a single flag: GUP_FLAGS_MUNLOCK ???
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Ying Han <yinghan@xxxxxxxxxx>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: Rohit Seth <rohitseth@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/internal.h | 1 +
mm/memory.c | 11 ++++++++---
mm/mlock.c | 9 +++++----
3 files changed, 14 insertions(+), 7 deletions(-)
diff -puN mm/internal.h~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock mm/internal.h
--- a/mm/internal.h~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock
+++ a/mm/internal.h
@@ -276,6 +276,7 @@ static inline void mminit_validate_memmo
#define GUP_FLAGS_WRITE 0x1
#define GUP_FLAGS_FORCE 0x2
#define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
+#define GUP_FLAGS_IGNORE_SIGKILL 0x8
int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, int flags,
diff -puN mm/memory.c~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock mm/memory.c
--- a/mm/memory.c~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock
+++ a/mm/memory.c
@@ -1197,6 +1197,7 @@ int __get_user_pages(struct task_struct
int write = !!(flags & GUP_FLAGS_WRITE);
int force = !!(flags & GUP_FLAGS_FORCE);
int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
+ int ignore_sigkill = !!(flags & GUP_FLAGS_IGNORE_SIGKILL);
if (len <= 0)
return 0;
@@ -1275,10 +1276,14 @@ int __get_user_pages(struct task_struct
struct page *page;
/*
- * If we have a pending SIGKILL, don't keep
- * allocating memory.
+ * If we have a pending SIGKILL, don't keep faulting
+ * pages and potentially allocating memory, unless
+ * current is handling munlock--e.g., on exit. In
+ * that case, we are not allocating memory. Rather,
+ * we're only unlocking already resident/mapped pages.
*/
- if (unlikely(fatal_signal_pending(current)))
+ if (unlikely(!ignore_sigkill &&
+ fatal_signal_pending(current)))
return i ? i : -ERESTARTSYS;
if (write)
diff -puN mm/mlock.c~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock mm/mlock.c
--- a/mm/mlock.c~mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock
+++ a/mm/mlock.c
@@ -173,12 +173,13 @@ static long __mlock_vma_pages_range(stru
(atomic_read(&mm->mm_users) != 0));
/*
- * mlock: don't page populate if page has PROT_NONE permission.
- * munlock: the pages always do munlock althrough
- * its has PROT_NONE permission.
+ * mlock: don't page populate if vma has PROT_NONE permission.
+ * munlock: always do munlock although the vma has PROT_NONE
+ * permission, or SIGKILL is pending.
*/
if (!mlock)
- gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS;
+ gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS |
+ GUP_FLAGS_IGNORE_SIGKILL;
if (vma->vm_flags & VM_WRITE)
gup_flags |= GUP_FLAGS_WRITE;
_
Patches currently in -mm which might be from Lee.Schermerhorn@xxxxxx are
cleanup-get-rid-of-ifdef-config_migration.patch
mm-add_active_or_unevictable-into-rmap.patch
vmscan-shrink_active_list-reduce-lru_lock-hold-time.patch
mm-make-get_user_pages-interruptible-mmotm-ignore-sigkill-in-get_user_pages-during-munlock.patch
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