From 4779280d1ea4d361af13ae77ba55217fbcd16d4c Mon Sep 17 00:00:00 2001 From: Ying Han Date: Tue, 6 Jan 2009 14:40:18 -0800 Subject: 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 Signed-off-by: Ying Han Reviewed-by: KOSAKI Motohiro Reviewed-by: Pekka Enberg Cc: Nick Piggin Cc: Hugh Dickins Cc: Oleg Nesterov Cc: Lee Schermerhorn Cc: Rohit Seth Cc: David Rientjes Signed-off-by: Lee Schermerhorn Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index db68af8e0bc4..3f8fa06b963b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1210,6 +1210,7 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 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 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, 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; -- cgit v1.2.1