afs: Re-enable freezing once a page fault is interrupted

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@infradead.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20210616154900.1958373-1-willy@infradead.org/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/afs/write.c b/fs/afs/write.c
index a523bb8..e9ccaa3 100644 (file)
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -837,6 +837,7 @@ 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);
 
@@ -848,14 +849,14 @@ 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
@@ -863,7 +864,7 @@ 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));
@@ -877,8 +878,10 @@ 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;
 }
 
 /*