linux-ext4 - [PATCH 3/3] ext4: Take read lock during overwrite case.

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Message-Id: <1197647297-7009-4-git-send-email-aneesh.kumar@linux.vnet.ibm.com>
Date:	Fri, 14 Dec 2007 21:18:17 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	cmm@...ibm.com, tytso@....edu
Cc:	linux-ext4@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH 3/3] ext4: Take read  lock during overwrite case.

When we are overwriting a file and not actually allocating new file system
blocks we need to take only the read lock on i_data_sem.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
---
 fs/ext4/inode.c |   32 ++++++++++++++++++++++++--------
 1 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 669d560..7dda65d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -895,11 +895,31 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
 			int create, int extend_disksize)
 {
 	int retval;
-	if (create) {
-		down_write((&EXT4_I(inode)->i_data_sem));
+	/*
+	 * Try to see if we can get  the block without requesting
+	 * for new file system block.
+	 */
+	down_read((&EXT4_I(inode)->i_data_sem));
+	if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
+		retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
+				bh, 0, 0);
 	} else {
-		down_read((&EXT4_I(inode)->i_data_sem));
+		retval =  ext4_get_blocks_handle(handle, inode, block, max_blocks,
+				bh, 0, 0);
 	}
+	up_read((&EXT4_I(inode)->i_data_sem));
+	if (!create || (retval > 0))
+		return retval;
+
+	/*
+	 * We need to allocate new blocks which will result
+	 * in i_data update
+	 */
+	down_write((&EXT4_I(inode)->i_data_sem));
+	/*
+	 * We need to check for EXT4 here because migrate
+	 * could have changed the inode type in between
+	 */
 	if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
 		retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
 				bh, create, extend_disksize);
@@ -907,11 +927,7 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
 		retval =  ext4_get_blocks_handle(handle, inode, block, max_blocks,
 				bh, create, extend_disksize);
 	}
-	if (create) {
-		up_write((&EXT4_I(inode)->i_data_sem));
-	} else {
-		up_read((&EXT4_I(inode)->i_data_sem));
-	}
+	up_write((&EXT4_I(inode)->i_data_sem));
 	return retval;
 }
 static int ext4_get_block(struct inode *inode, sector_t iblock,
-- 
1.5.4.rc0-dirty

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