linux-kernel - [PATCH] afs: Re-enable freezing once a page fault is interrupted

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Message-ID: <162387854886.1035841.15139736369962171742.stgit@warthog.procyon.org.uk>
Date:   Wed, 16 Jun 2021 22:22:28 +0100
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        linux-afs@...ts.infradead.org, dhowells@...hat.com,
        marc.dionne@...istor.com, linux-afs@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Re-enable freezing once a page fault is interrupted

From: Matthew Wilcox (Oracle) <willy@...radead.org>

If a task is killed during a page fault, it does not currently call
sb_end_pagefault(), which means that the filesystem cannot be frozen
at any time thereafter.  This may be reported by lockdep like this:

====================================
WARNING: fsstress/10757 still has locks held!
5.13.0-rc4-build4+ #91 Not tainted
------------------------------------
1 lock held by fsstress/10757:
 #0: ffff888104eac530
 (
sb_pagefaults

as filesystem freezing is modelled as a lock.

Fix this by removing all the direct returns from within the function,
and using 'ret' to indicate whether we were interrupted or successful.

Fixes: 1cf7a1518aef ("afs: Implement shared-writeable mmap")
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: David Howells <dhowells@...hat.com>
cc: linux-afs@...ts.infradead.org
Link: https://lore.kernel.org/r/20210616154900.1958373-1-willy@infradead.org/
---

 fs/afs/write.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index f722cb80a594..ff36800a7389 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -848,6 +848,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	struct inode *inode = file_inode(file);
 	struct afs_vnode *vnode = AFS_FS_I(inode);
 	unsigned long priv;
+	vm_fault_t ret = VM_FAULT_RETRY;
 
 	_enter("{{%llx:%llu}},{%lx}", vnode->fid.vid, vnode->fid.vnode, page->index);
 
@@ -859,14 +860,14 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 #ifdef CONFIG_AFS_FSCACHE
 	if (PageFsCache(page) &&
 	    wait_on_page_fscache_killable(page) < 0)
-		return VM_FAULT_RETRY;
+		goto out;
 #endif
 
 	if (wait_on_page_writeback_killable(page))
-		return VM_FAULT_RETRY;
+		goto out;
 
 	if (lock_page_killable(page) < 0)
-		return VM_FAULT_RETRY;
+		goto out;
 
 	/* We mustn't change page->private until writeback is complete as that
 	 * details the portion of the page we need to write back and we might
@@ -874,7 +875,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	 */
 	if (wait_on_page_writeback_killable(page) < 0) {
 		unlock_page(page);
-		return VM_FAULT_RETRY;
+		goto out;
 	}
 
 	priv = afs_page_dirty(page, 0, thp_size(page));
@@ -888,8 +889,10 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	}
 	file_update_time(file);
 
+	ret = VM_FAULT_LOCKED;
+out:
 	sb_end_pagefault(inode->i_sb);
-	return VM_FAULT_LOCKED;
+	return ret;
 }
 
 /*