linux-ext4 - [PATCH] ext4: make it possible to interrupt initial readdir call

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Message-ID: <20160314175732.GL17923@kvack.org>
Date:	Mon, 14 Mar 2016 13:57:32 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org
Subject: [PATCH] ext4: make it possible to interrupt initial readdir call

This patch is a follow up to the email "ext4 bug: getdents uninterruptible 
for 117 seconds".  When doing the initial readdir on an ext4 filesystem 
that grew a directory to 497MB (the filesystem image can be downloaded at
http://www.kvack.org/~bcrl/ext4/ext4-readdir.img.xz), the first getdents64() 
system call blocked for 117 seconds.  Begin to address this issue by making 
the ext4 readdir() operation interruptible by fatal signals so that it is 
possible to abort a process that is stuck on this operation.

 fs/ext4/dir.c   |    3 +++
 fs/ext4/namei.c |    4 ++++
 2 files changed, 7 insertions(+)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 33f5e2a..a3e32e8 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -553,6 +553,9 @@ static int ext4_dx_readdir(struct file *file, struct dir_context *ctx)
 		info->curr_node = rb_first(&info->root);
 
 	while (1) {
+		if (fatal_signal_pending(current))
+			return -ERESTARTSYS;
+
 		/*
 		 * Fill the rbtree if we have no more entries,
 		 * or the inode has changed since we last read in the
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 48e4b89..8097cd1 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -959,6 +959,10 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 	bh = ext4_read_dirblock(dir, block, DIRENT);
 	if (IS_ERR(bh))
 		return PTR_ERR(bh);
+	if (fatal_signal_pending(current)) {
+		brelse(bh);
+		return -ERESTARTSYS;
+	}
 
 	de = (struct ext4_dir_entry_2 *) bh->b_data;
 	top = (struct ext4_dir_entry_2 *) ((char *) de +
-- 
"Thought is the essence of where you are now."
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