mm: make get_user_pages() interruptible
The initial implementation of checking TIF_MEMDIE covers the cases of OOM
killing. If the process has been OOM killed, the TIF_MEMDIE is set and it
return immediately. This patch includes:
1. add the case that the SIGKILL is sent by user processes. The
process can try to get_user_pages() unlimited memory even if a user
process has sent a SIGKILL to it(maybe a monitor find the process
exceed its memory limit and try to kill it). In the old
implementation, the SIGKILL won't be handled until the get_user_pages()
returns.
2. change the return value to be ERESTARTSYS. It makes no sense to
return ENOMEM if the get_user_pages returned by getting a SIGKILL
signal. Considering the general convention for a system call
interrupted by a signal is ERESTARTNOSYS, so the current return value
is consistant to that.
Lee:
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 ???
[Lee.Schermerhorn@hp.com: ignore sigkill in get_user_pages during munlock]
Signed-off-by: Paul Menage <menage@google.com>
Signed-off-by: Ying Han <yinghan@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Rohit Seth <rohitseth@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/internal.h b/mm/internal.h
index 1981bc9..478223b 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -276,6 +276,7 @@
#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 --git a/mm/memory.c b/mm/memory.c
index db68af8..3f8fa06 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1210,6 +1210,7 @@
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;
@@ -1288,12 +1289,15 @@
struct page *page;
/*
- * If tsk is ooming, cut off its access to large memory
- * allocations. It has a pending SIGKILL, but it can't
- * be processed until returning to user space.
+ * 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(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
- return i ? i : -ENOMEM;
+ if (unlikely(!ignore_sigkill &&
+ fatal_signal_pending(current)))
+ return i ? i : -ERESTARTSYS;
if (write)
foll_flags |= FOLL_WRITE;
diff --git a/mm/mlock.c b/mm/mlock.c
index 3035a56..e125156 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -173,12 +173,13 @@
(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;