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[70.31.26.132]) by smtp.gmail.com with ESMTPSA id x13-20020ac8120d000000b003a6847d6386sm1483787qti.68.2022.12.16.07.52.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Dec 2022 07:52:18 -0800 (PST) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: David Hildenbrand , John Hubbard , Muchun Song , Mike Kravetz , Nadav Amit , Andrea Arcangeli , Rik van Riel , peterx@redhat.com, Miaohe Lin , Jann Horn , James Houghton , Andrew Morton Subject: [PATCH v4 5/9] mm/hugetlb: Make userfaultfd_huge_must_wait() safe to pmd unshare Date: Fri, 16 Dec 2022 10:52:17 -0500 Message-Id: <20221216155217.2043700-1-peterx@redhat.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221216155100.2043537-1-peterx@redhat.com> References: <20221216155100.2043537-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We can take the hugetlb walker lock, here taking vma lock directly. Reviewed-by: David Hildenbrand Reviewed-by: Mike Kravetz Reviewed-by: John Hubbard Signed-off-by: Peter Xu --- fs/userfaultfd.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 98ac37e34e3d..887e20472051 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -376,7 +376,8 @@ static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags) */ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) { - struct mm_struct *mm = vmf->vma->vm_mm; + struct vm_area_struct *vma = vmf->vma; + struct mm_struct *mm = vma->vm_mm; struct userfaultfd_ctx *ctx; struct userfaultfd_wait_queue uwq; vm_fault_t ret = VM_FAULT_SIGBUS; @@ -403,7 +404,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) */ mmap_assert_locked(mm); - ctx = vmf->vma->vm_userfaultfd_ctx.ctx; + ctx = vma->vm_userfaultfd_ctx.ctx; if (!ctx) goto out; @@ -493,6 +494,15 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) blocking_state = userfaultfd_get_blocking_state(vmf->flags); + /* + * Take the vma lock now, in order to safely call + * userfaultfd_huge_must_wait() later. Since acquiring the + * (sleepable) vma lock can modify the current task state, that + * must be before explicitly calling set_current_state(). + */ + if (is_vm_hugetlb_page(vma)) + hugetlb_vma_lock_read(vma); + spin_lock_irq(&ctx->fault_pending_wqh.lock); /* * After the __add_wait_queue the uwq is visible to userland @@ -507,13 +517,15 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) set_current_state(blocking_state); spin_unlock_irq(&ctx->fault_pending_wqh.lock); - if (!is_vm_hugetlb_page(vmf->vma)) + if (!is_vm_hugetlb_page(vma)) must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags, reason); else - must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma, + must_wait = userfaultfd_huge_must_wait(ctx, vma, vmf->address, vmf->flags, reason); + if (is_vm_hugetlb_page(vma)) + hugetlb_vma_unlock_read(vma); mmap_read_unlock(mm); if (likely(must_wait && !READ_ONCE(ctx->released))) { -- 2.37.3