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>
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4779280d1e
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@ -276,6 +276,7 @@ static inline void mminit_validate_memmodel_limits(unsigned long *start_pfn,
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#define GUP_FLAGS_WRITE 0x1
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#define GUP_FLAGS_FORCE 0x2
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#define GUP_FLAGS_IGNORE_VMA_PERMISSIONS 0x4
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#define GUP_FLAGS_IGNORE_SIGKILL 0x8
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int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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unsigned long start, int len, int flags,
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14
mm/memory.c
14
mm/memory.c
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@ -1210,6 +1210,7 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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int write = !!(flags & GUP_FLAGS_WRITE);
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int force = !!(flags & GUP_FLAGS_FORCE);
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int ignore = !!(flags & GUP_FLAGS_IGNORE_VMA_PERMISSIONS);
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int ignore_sigkill = !!(flags & GUP_FLAGS_IGNORE_SIGKILL);
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if (len <= 0)
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return 0;
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@ -1288,12 +1289,15 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
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struct page *page;
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/*
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* If tsk is ooming, cut off its access to large memory
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* allocations. It has a pending SIGKILL, but it can't
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* be processed until returning to user space.
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* If we have a pending SIGKILL, don't keep faulting
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* pages and potentially allocating memory, unless
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* current is handling munlock--e.g., on exit. In
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* that case, we are not allocating memory. Rather,
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* we're only unlocking already resident/mapped pages.
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*/
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if (unlikely(test_tsk_thread_flag(tsk, TIF_MEMDIE)))
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return i ? i : -ENOMEM;
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if (unlikely(!ignore_sigkill &&
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fatal_signal_pending(current)))
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return i ? i : -ERESTARTSYS;
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if (write)
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foll_flags |= FOLL_WRITE;
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@ -173,12 +173,13 @@ static long __mlock_vma_pages_range(struct vm_area_struct *vma,
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(atomic_read(&mm->mm_users) != 0));
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/*
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* mlock: don't page populate if page has PROT_NONE permission.
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* munlock: the pages always do munlock althrough
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* its has PROT_NONE permission.
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* mlock: don't page populate if vma has PROT_NONE permission.
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* munlock: always do munlock although the vma has PROT_NONE
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* permission, or SIGKILL is pending.
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*/
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if (!mlock)
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gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS;
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gup_flags |= GUP_FLAGS_IGNORE_VMA_PERMISSIONS |
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GUP_FLAGS_IGNORE_SIGKILL;
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if (vma->vm_flags & VM_WRITE)
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gup_flags |= GUP_FLAGS_WRITE;
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