linux-ext4 - Re: [PATCH 03/14] mm: Protect operations adding pages to page cache with invalidate

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Date:   Tue, 13 Jul 2021 07:25:05 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Ted Tso <tytso@....edu>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 03/14] mm: Protect operations adding pages to page cache
 with invalidate_lock

Still looks good.  That being said the additional conditional locking in
filemap_fault makes it fall over the readbility cliff for me.  Something
like this on top of your series would help:

diff --git a/mm/filemap.c b/mm/filemap.c
index fd3f94d36c49..0fad08331cf4 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3040,21 +3040,23 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 	 * Do we have something in the page cache already?
 	 */
 	page = find_get_page(mapping, offset);
-	if (likely(page) && !(vmf->flags & FAULT_FLAG_TRIED)) {
+	if (likely(page)) {
 		/*
-		 * We found the page, so try async readahead before
-		 * waiting for the lock.
+		 * We found the page, so try async readahead before waiting for
+		 * the lock.
 		 */
-		fpin = do_async_mmap_readahead(vmf, page);
-	} else if (!page) {
+		if (!(vmf->flags & FAULT_FLAG_TRIED))
+			fpin = do_async_mmap_readahead(vmf, page);
+		if (unlikely(!PageUptodate(page))) {
+			filemap_invalidate_lock_shared(mapping);
+			mapping_locked = true;
+		}
+	} else {
 		/* No page in the page cache at all */
 		count_vm_event(PGMAJFAULT);
 		count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
 		ret = VM_FAULT_MAJOR;
 		fpin = do_sync_mmap_readahead(vmf);
-	}
-
-	if (!page) {
 retry_find:
 		/*
 		 * See comment in filemap_create_page() why we need
@@ -3073,9 +3075,6 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 			filemap_invalidate_unlock_shared(mapping);
 			return VM_FAULT_OOM;
 		}
-	} else if (unlikely(!PageUptodate(page))) {
-		filemap_invalidate_lock_shared(mapping);
-		mapping_locked = true;
 	}
 
 	if (!lock_page_maybe_drop_mmap(vmf, page, &fpin))