linux-kernel - [PATCH 1/2] mm: Change vmf_anon_prepare() to __vmf_anon

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Message-ID: <20240914194243.245-1-vishal.moola@gmail.com>
Date: Sat, 14 Sep 2024 12:41:18 -0700
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: Muchun Song <muchun.song@...ux.dev>,
	syzbot <syzbot+2dab93857ee95f2eeb08@...kaller.appspotmail.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	syzkaller-bugs@...glegroups.com
Cc: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: [PATCH 1/2] mm: Change vmf_anon_prepare() to __vmf_anon_prepare()

Some callers of vmf_anon_prepare() may not want us to release the
per-VMA lock ourselves. Rename vmf_anon_prepare() to
__vmf_anon_prepare() and let the callers drop the lock when desired.

Also, make vmf_anon_prepare() a wrapper that releases the per-VMA lock
itself for any callers that don't care.

This is in preparation to fix this bug reported by syzbot:
https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@google.com/

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
---
 mm/internal.h | 11 ++++++++++-
 mm/memory.c   |  8 +++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 44c8dec1f0d7..93083bbeeefa 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -320,7 +320,16 @@ static inline void wake_throttle_isolated(pg_data_t *pgdat)
 		wake_up(wqh);
 }
 
-vm_fault_t vmf_anon_prepare(struct vm_fault *vmf);
+vm_fault_t __vmf_anon_prepare(struct vm_fault *vmf);
+static inline vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
+{
+	vm_fault_t ret = __vmf_anon_prepare(vmf);
+
+	if (unlikely(ret & VM_FAULT_RETRY))
+		vma_end_read(vmf->vma);
+	return ret;
+}
+
 vm_fault_t do_swap_page(struct vm_fault *vmf);
 void folio_rotate_reclaimable(struct folio *folio);
 bool __folio_end_writeback(struct folio *folio);
diff --git a/mm/memory.c b/mm/memory.c
index 36f655eb66c4..d564737255f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3262,7 +3262,7 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
 }
 
 /**
- * vmf_anon_prepare - Prepare to handle an anonymous fault.
+ * __vmf_anon_prepare - Prepare to handle an anonymous fault.
  * @vmf: The vm_fault descriptor passed from the fault handler.
  *
  * When preparing to insert an anonymous page into a VMA from a
@@ -3276,7 +3276,7 @@ static inline vm_fault_t vmf_can_call_fault(const struct vm_fault *vmf)
  * Return: 0 if fault handling can proceed.  Any other value should be
  * returned to the caller.
  */
-vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
+vm_fault_t __vmf_anon_prepare(struct vm_fault *vmf)
 {
 	struct vm_area_struct *vma = vmf->vma;
 	vm_fault_t ret = 0;
@@ -3284,10 +3284,8 @@ vm_fault_t vmf_anon_prepare(struct vm_fault *vmf)
 	if (likely(vma->anon_vma))
 		return 0;
 	if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
-		if (!mmap_read_trylock(vma->vm_mm)) {
-			vma_end_read(vma);
+		if (!mmap_read_trylock(vma->vm_mm))
 			return VM_FAULT_RETRY;
-		}
 	}
 	if (__anon_vma_prepare(vma))
 		ret = VM_FAULT_OOM;
-- 
2.45.0