From: Peter Xu <pet...@redhat.com> Patch series "mm: Page fault enhancements", v6.
This series contains cleanups and enhancements to current page fault logic. The whole idea comes from the discussion between Andrea and Linus on the bug reported by syzbot here: https://lkml.org/lkml/2017/11/2/833 Basically it does two things: (a) Allows the page fault logic to be more interactive on not only SIGKILL, but also the rest of userspace signals, and, (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more than once. For (a): with the changes we should be able to react faster when page faults are working in parallel with userspace signals like SIGSTOP and SIGCONT (and more), and with that we can remove the buggy part in userfaultfd and benefit the whole page fault mechanism on faster signal processing to reach the userspace. For (b), we should be able to allow the page fault handler to loop for even more than twice. Some context: for now since we have FAULT_FLAG_ALLOW_RETRY we can allow to retry the page fault once with the same interrupt context, however never more than twice. This can be not only a potential cleanup to remove this assumption since AFAIU the code itself doesn't really have this twice-only limitation (though that should be a protective approach in the past), at the same time it'll greatly simplify future works like userfaultfd write-protect where it's possible to retry for more than twice (please have a look at [1] below for a possible user that might require the page fault to be handled for a third time; if we can remove the retry limitation we can simply drop that patch and those complexity). This patch (of 16): There's plenty of places around __get_user_pages() that has a parameter "nonblocking" which does not really mean that "it won't block" (because it can really block) but instead it shows whether the mmap_sem is released by up_read() during the page fault handling mostly when VM_FAULT_RETRY is returned. We have the correct naming in e.g. get_user_pages_locked() or get_user_pages_remote() as "locked", however there're still many places that are using the "nonblocking" as name. Renaming the places to "locked" where proper to better suite the functionality of the variable. While at it, fixing up some of the comments accordingly. Signed-off-by: Peter Xu <pet...@redhat.com> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Tested-by: Brian Geffon <bgef...@google.com> Reviewed-by: Mike Rapoport <r...@linux.vnet.ibm.com> Reviewed-by: Jerome Glisse <jgli...@redhat.com> Reviewed-by: David Hildenbrand <da...@redhat.com> Cc: Andrea Arcangeli <aarca...@redhat.com> Cc: Martin Cracauer <craca...@cons.org> Cc: "Kirill A . Shutemov" <kir...@shutemov.name> Cc: Johannes Weiner <han...@cmpxchg.org> Cc: "Dr . David Alan Gilbert" <dgilb...@redhat.com> Cc: Bobby Powers <bobbypow...@gmail.com> Cc: Maya Gokhale <gokha...@llnl.gov> Cc: Mike Kravetz <mike.krav...@oracle.com> Cc: Matthew Wilcox <wi...@infradead.org> Cc: Marty McFadden <mcfadd...@llnl.gov> Cc: Mel Gorman <mgor...@suse.de> Cc: Hugh Dickins <hu...@google.com> Cc: Denis Plotnikov <dplotni...@virtuozzo.com> Cc: Pavel Emelyanov <xe...@openvz.org> Link: http://lkml.kernel.org/r/20200220155353.8676-2-pet...@redhat.com Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> https://jira.sw.ru/browse/PSBM-102938 (cherry picked from commit 4f6da93411806db2f3e58193b31b95e8c6737616) Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- mm/gup.c | 44 +++++++++++++++++++++----------------------- mm/hugetlb.c | 8 ++++---- 2 files changed, 25 insertions(+), 27 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index fc5f98069f4e..f609ac36aa9a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -489,12 +489,12 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address, } /* - * mmap_sem must be held on entry. If @nonblocking != NULL and - * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released. - * If it is, *@nonblocking will be set to 0 and -EBUSY returned. + * mmap_sem must be held on entry. If @locked != NULL and *@flags + * does not include FOLL_NOWAIT, the mmap_sem may be released. If it + * is, *@locked will be set to 0 and -EBUSY returned. */ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, - unsigned long address, unsigned int *flags, int *nonblocking) + unsigned long address, unsigned int *flags, int *locked) { unsigned int fault_flags = 0; int ret; @@ -506,7 +506,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, fault_flags |= FAULT_FLAG_WRITE; if (*flags & FOLL_REMOTE) fault_flags |= FAULT_FLAG_REMOTE; - if (nonblocking) + if (locked) fault_flags |= FAULT_FLAG_ALLOW_RETRY; if (*flags & FOLL_NOWAIT) fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT; @@ -532,8 +532,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, } if (ret & VM_FAULT_RETRY) { - if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT)) - *nonblocking = 0; + if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT)) + *locked = 0; return -EBUSY; } @@ -610,7 +610,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) * only intends to ensure the pages are faulted in. * @vmas: array of pointers to vmas corresponding to each page. * Or NULL if the caller does not require them. - * @nonblocking: whether waiting for disk IO or mmap_sem contention + * @locked: whether we're still with the mmap_sem held * * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages @@ -639,13 +639,11 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) * appropriate) must be called after the page is finished with, and * before put_page is called. * - * If @nonblocking != NULL, __get_user_pages will not wait for disk IO - * or mmap_sem contention, and if waiting is needed to pin all pages, - * *@nonblocking will be set to 0. Further, if @gup_flags does not - * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in - * this case. + * If @locked != NULL, *@locked will be set to 0 when mmap_sem is + * released by an up_read(). That can happen if @gup_flags does not + * have FOLL_NOWAIT. * - * A caller using such a combination of @nonblocking and @gup_flags + * A caller using such a combination of @locked and @gup_flags * must therefore hold the mmap_sem for reading only, and recognize * when it's been released. Otherwise, it must be held for either * reading or writing and will not be released. @@ -657,7 +655,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, - struct vm_area_struct **vmas, int *nonblocking) + struct vm_area_struct **vmas, int *locked) { long i = 0; unsigned int page_mask; @@ -700,7 +698,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, if (is_vm_hugetlb_page(vma)) { i = follow_hugetlb_page(mm, vma, pages, vmas, &start, &nr_pages, i, - gup_flags, nonblocking); + gup_flags, locked); continue; } } @@ -716,7 +714,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, if (!page) { int ret; ret = faultin_page(tsk, vma, start, &foll_flags, - nonblocking); + locked); switch (ret) { case 0: goto retry; @@ -1170,7 +1168,7 @@ EXPORT_SYMBOL(get_user_pages_longterm); * @vma: target vma * @start: start address * @end: end address - * @nonblocking: + * @locked: whether the mmap_sem is still held * * This takes care of mlocking the pages too if VM_LOCKED is set. * @@ -1178,14 +1176,14 @@ EXPORT_SYMBOL(get_user_pages_longterm); * * vma->vm_mm->mmap_sem must be held. * - * If @nonblocking is NULL, it may be held for read or write and will + * If @locked is NULL, it may be held for read or write and will * be unperturbed. * - * If @nonblocking is non-NULL, it must held for read only and may be - * released. If it's released, *@nonblocking will be set to 0. + * If @locked is non-NULL, it must held for read only and may be + * released. If it's released, *@locked will be set to 0. */ long populate_vma_page_range(struct vm_area_struct *vma, - unsigned long start, unsigned long end, int *nonblocking) + unsigned long start, unsigned long end, int *locked) { struct mm_struct *mm = vma->vm_mm; unsigned long nr_pages = (end - start) / PAGE_SIZE; @@ -1220,7 +1218,7 @@ long populate_vma_page_range(struct vm_area_struct *vma, * not result in a stack expansion that recurses back here. */ return __get_user_pages(current, mm, start, nr_pages, gup_flags, - NULL, NULL, nonblocking); + NULL, NULL, locked); } /* diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 14edbb3c0fc7..1c6584c8e78e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4151,7 +4151,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm, long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, struct page **pages, struct vm_area_struct **vmas, unsigned long *position, unsigned long *nr_pages, - long i, unsigned int flags, int *nonblocking) + long i, unsigned int flags, int *locked) { unsigned long pfn_offset; unsigned long vaddr = *position; @@ -4222,7 +4222,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, spin_unlock(ptl); if (flags & FOLL_WRITE) fault_flags |= FAULT_FLAG_WRITE; - if (nonblocking) + if (locked) fault_flags |= FAULT_FLAG_ALLOW_RETRY; if (flags & FOLL_NOWAIT) fault_flags |= FAULT_FLAG_ALLOW_RETRY | @@ -4239,9 +4239,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma, break; } if (ret & VM_FAULT_RETRY) { - if (nonblocking && + if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT)) - *nonblocking = 0; + *locked = 0; *nr_pages = 0; /* * VM_FAULT_RETRY must not return an -- 2.25.3 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel
