ipc/shm: use VMA iterator instead of linked list

The VMA iterator is faster than the linked llist, and it can be walked
even when VMAs are being removed from the address space, so there's no
need to keep track of 'next'.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Liam R. Howlett <[email protected]>
Tested-by: Yu Zhao <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Howells <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 10 insertions, 11 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index b3048ebd5c31..7d86f058fb86 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1721,7 +1721,7 @@ long ksys_shmdt(char __user *shmaddr)
 #ifdef CONFIG_MMU
 	loff_t size = 0;
 	struct file *file;
-	struct vm_area_struct *next;
+	VMA_ITERATOR(vmi, mm, addr);
 #endif
 
 	if (addr & ~PAGE_MASK)
@@ -1751,12 +1751,9 @@ long ksys_shmdt(char __user *shmaddr)
 	 * match the usual checks anyway. So assume all vma's are
 	 * above the starting address given.
 	 */
-	vma = find_vma(mm, addr);
 
 #ifdef CONFIG_MMU
-	while (vma) {
-		next = vma->vm_next;
-
+	for_each_vma(vmi, vma) {
 		/*
 		 * Check if the starting address would match, i.e. it's
 		 * a fragment created by mprotect() and/or munmap(), or it
@@ -1774,6 +1771,7 @@ long ksys_shmdt(char __user *shmaddr)
 			file = vma->vm_file;
 			size = i_size_read(file_inode(vma->vm_file));
 			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
+			mas_pause(&vmi.mas);
 			/*
 			 * We discovered the size of the shm segment, so
 			 * break out of here and fall through to the next
@@ -1781,10 +1779,9 @@ long ksys_shmdt(char __user *shmaddr)
 			 * searching for matching vma's.
 			 */
 			retval = 0;
-			vma = next;
+			vma = vma_next(&vmi);
 			break;
 		}
-		vma = next;
 	}
 
 	/*
@@ -1794,17 +1791,19 @@ long ksys_shmdt(char __user *shmaddr)
 	 */
 	size = PAGE_ALIGN(size);
 	while (vma && (loff_t)(vma->vm_end - addr) <= size) {
-		next = vma->vm_next;
-
 		/* finding a matching vma now does not alter retval */
 		if ((vma->vm_ops == &shm_vm_ops) &&
 		    ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
-		    (vma->vm_file == file))
+		    (vma->vm_file == file)) {
 			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
-		vma = next;
+			mas_pause(&vmi.mas);
+		}
+
+		vma = vma_next(&vmi);
 	}
 
 #else	/* CONFIG_MMU */
+	vma = vma_lookup(mm, addr);
 	/* under NOMMU conditions, the exact address to be destroyed must be
 	 * given
 	 */