From: "Matthew Wilcox (Oracle)" <willy@infradead.org> mainline inclusion from mainline-v6.7-rc1 commit 4ed4379881aa62588aba6442a9f362a8cf7624e6 category: other bugzilla: https://gitee.com/openeuler/kernel/issues/I8K7C7 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- There are many implementations of ->fault and some of them depend on mmap_lock being held. All vm_ops that implement ->map_pages() end up calling filemap_fault(), which I have audited to be sure it does not rely on mmap_lock. So (for now) key off ->map_pages existing as a flag to indicate that it's safe to call ->fault while only holding the vma lock. Link: https://lkml.kernel.org/r/20231006195318.4087158-4-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com> --- mm/memory.c | 22 ++++++++++++++++++---- 1 file changed, 18 insertions(+), 4 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 73cbca4ed65d..f5ac37abdb06 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3044,6 +3044,21 @@ static inline void wp_page_reuse(struct vm_fault *vmf, struct folio *folio) count_vm_event(PGREUSE); } +/* + * We could add a bitflag somewhere, but for now, we know that all + * vm_ops that have a ->map_pages have been audited and don't need + * the mmap_lock to be held. + */ +static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf) +{ + struct vm_area_struct *vma = vmf->vma; + + if (vma->vm_ops->map_pages || !(vmf->flags & FAULT_FLAG_VMA_LOCK)) + return 0; + vma_end_read(vma); + return VM_FAULT_RETRY; +} + static vm_fault_t vmf_anon_prepare(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; @@ -4655,10 +4670,9 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf) vm_fault_t ret, tmp; struct folio *folio; - if (vmf->flags & FAULT_FLAG_VMA_LOCK) { - vma_end_read(vma); - return VM_FAULT_RETRY; - } + ret = vmf_can_call_fault(vmf); + if (ret) + return ret; ret = __do_fault(vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY))) -- 2.25.1