Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 26 Jun 2023 21:23:16 -0700
In-Reply-To: <20230627042321.1763765-1-surenb@google.com>
Mime-Version: 1.0
References: <20230627042321.1763765-1-surenb@google.com>
Message-ID: <20230627042321.1763765-4-surenb@google.com>
Subject: [PATCH v3 3/8] mm: drop per-VMA lock in handle_mm_fault if retrying
 or when finished
From:   Suren Baghdasaryan <surenb@google.com>
To:     akpm@linux-foundation.org
Cc:     willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com,
        josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com,
        laurent.dufour@fr.ibm.com, michel@lespinasse.org,
        liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz,
        minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com,
        lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com,
        peterx@redhat.com, ying.huang@intel.com, david@redhat.com,
        yuzhao@google.com, dhowells@redhat.com, hughd@google.com,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        pasha.tatashin@soleen.com, surenb@google.com, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@android.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

handle_mm_fault returning VM_FAULT_RETRY or VM_FAULT_COMPLETED means
mmap_lock has been released. However with per-VMA locks behavior is
different and the caller should still release it. To make the
rules consistent for the caller, drop the per-VMA lock before returning
from handle_mm_fault when page fault should be retried or is completed.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 arch/arm64/mm/fault.c   |  3 ++-
 arch/powerpc/mm/fault.c |  3 ++-
 arch/s390/mm/fault.c    |  3 ++-
 arch/x86/mm/fault.c     |  3 ++-
 mm/memory.c             | 12 +++++++++++-
 5 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 6045a5117ac1..89f84e9ea1ff 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -601,7 +601,8 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
 		goto lock_mmap;
 	}
 	fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
-	vma_end_read(vma);
+	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+		vma_end_read(vma);
 
 	if (!(fault & VM_FAULT_RETRY)) {
 		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 531177a4ee08..4697c5dca31c 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -494,7 +494,8 @@ static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
 	}
 
 	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
-	vma_end_read(vma);
+	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+		vma_end_read(vma);
 
 	if (!(fault & VM_FAULT_RETRY)) {
 		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index b65144c392b0..cccefe41038b 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -418,7 +418,8 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 		goto lock_mmap;
 	}
 	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
-	vma_end_read(vma);
+	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+		vma_end_read(vma);
 	if (!(fault & VM_FAULT_RETRY)) {
 		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
 		goto out;
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e4399983c50c..d69c85c1c04e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1347,7 +1347,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 		goto lock_mmap;
 	}
 	fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
-	vma_end_read(vma);
+	if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
+		vma_end_read(vma);
 
 	if (!(fault & VM_FAULT_RETRY)) {
 		count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
diff --git a/mm/memory.c b/mm/memory.c
index f69fbc251198..9011ad63c41b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5086,7 +5086,17 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
 		}
 	}
 
-	return handle_pte_fault(&vmf);
+	ret = handle_pte_fault(&vmf);
+	if (ret & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)) {
+		/*
+		 * In case of VM_FAULT_RETRY or VM_FAULT_COMPLETED we might
+		 * be still holding per-VMA lock to keep the vma stable as long
+		 * as possible. Drop it before returning.
+		 */
+		if (vmf.flags & FAULT_FLAG_VMA_LOCK)
+			vma_end_read(vma);
+	}
+	return ret;
 }
 
 /**
-- 
2.41.0.178.g377b9f9a00-goog