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/

Link: https://lkml.kernel.org/r/20240914194243.245-1-vishal.moola@gmail.com
Fixes: 9acad7ba3e25 ("hugetlb: use vmf_anon_prepare() instead of anon_vma_prepare()")
Reported-by: syzbot+2dab93857ee95f2eeb08@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-mm/00000000000067c20b06219fbc26@google.com/
Signed-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/internal.h b/mm/internal.h
index b4d86436565b93a3c5773362f024652eea7b195b..a963f67d3452ada3992387b2bd9968f33b0a8429 100644 (file)
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -310,7 +310,16 @@ 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 3c01d68065be21a45d8b9085d7f81785bc5cbfd8..95c347ba630547ab43db1a1902afe62c9c506dfa 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3259,7 +3259,7 @@ 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
@@ -3273,7 +3273,7 @@ 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;
@@ -3281,10 +3281,8 @@ 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;