linux-kernel - [PATCH v4 44/66] ipc/shm: Use VMA iterator instead of linked list

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Message-ID: <20211201142918.921493-45-Liam.Howlett@oracle.com>
Date:   Wed, 1 Dec 2021 14:30:10 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
CC:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>
Subject: [PATCH v4 44/66] ipc/shm: Use VMA iterator instead of linked list

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

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'.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 ipc/shm.c | 21 ++++++++++-----------
 1 file 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
 	 */
-- 
2.30.2