[PATCH 2/2][SRU][E] Revert "Revert "ext4: make __ext4_get_inode_loc plug""

[Colin King]

From: Linus Torvalds <torvalds at linux-foundation.org>

BugLink: https://bugs.launchpad.net/bugs/1846486

This reverts commit 72dbcf72156641fde4d8ea401e977341bfd35a05.

Instead of waiting forever for entropy that may just not happen, we now
try to actively generate entropy when required, and are thus hopefully
avoiding the problem that caused the nice ext4 IO pattern fix to be
reverted.

So revert the revert.

Cc: Ahmed S. Darwish <darwish.07 at gmail.com>
Cc: Ted Ts'o <tytso at mit.edu>
Cc: Willy Tarreau <w at 1wt.eu>
Cc: Alexander E. Patrakov <patrakov at gmail.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit 02f03c4206c1b2a7451d3b3546f86c9c783eac13)
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 fs/ext4/inode.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index f2b2524..552a5fc 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4586,6 +4586,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
 	struct buffer_head	*bh;
 	struct super_block	*sb = inode->i_sb;
 	ext4_fsblk_t		block;
+	struct blk_plug		plug;
 	int			inodes_per_block, inode_offset;
 
 	iloc->bh = NULL;
@@ -4674,6 +4675,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
 		 * If we need to do any I/O, try to pre-readahead extra
 		 * blocks from the inode table.
 		 */
+		blk_start_plug(&plug);
 		if (EXT4_SB(sb)->s_inode_readahead_blks) {
 			ext4_fsblk_t b, end, table;
 			unsigned num;
@@ -4704,6 +4706,7 @@ static int __ext4_get_inode_loc(struct inode *inode,
 		get_bh(bh);
 		bh->b_end_io = end_buffer_read_sync;
 		submit_bh(REQ_OP_READ, REQ_META | REQ_PRIO, bh);
+		blk_finish_plug(&plug);
 		wait_on_buffer(bh);
 		if (!buffer_uptodate(bh)) {
 			EXT4_ERROR_INODE_BLOCK(inode, block,
-- 
2.7.4