linux-kernel - [PATCH] fix ufs write vs. readpage race when writing into a hole

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Date:	Wed, 9 Sep 2015 10:16:39 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH] fix ufs write vs. readpage race when writing into a hole

	Followup to UFS series - with the way we clear the new blocks (via
buffer cache, possibly on more than a page worth of file) we really should
not insert a reference to new block into inode block tree until after we'd
cleared it.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/fs/ufs/balloc.c b/fs/ufs/balloc.c
index fb8b54e..dc5fae6 100644
--- a/fs/ufs/balloc.c
+++ b/fs/ufs/balloc.c
@@ -417,14 +417,14 @@ u64 ufs_new_fragments(struct inode *inode, void *p, u64 fragment,
 	if (oldcount == 0) {
 		result = ufs_alloc_fragments (inode, cgno, goal, count, err);
 		if (result) {
+			ufs_clear_frags(inode, result + oldcount,
+					newcount - oldcount, locked_page != NULL);
 			write_seqlock(&UFS_I(inode)->meta_lock);
 			ufs_cpu_to_data_ptr(sb, p, result);
 			write_sequnlock(&UFS_I(inode)->meta_lock);
 			*err = 0;
 			UFS_I(inode)->i_lastfrag =
 				max(UFS_I(inode)->i_lastfrag, fragment + count);
-			ufs_clear_frags(inode, result + oldcount,
-					newcount - oldcount, locked_page != NULL);
 		}
 		mutex_unlock(&UFS_SB(sb)->s_lock);
 		UFSD("EXIT, result %llu\n", (unsigned long long)result);
--
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