From: Steven Whitehouse <swhiteho@redhat.com>
Subject: [RHEL5] bz 218966 Use try locks [3/4]
Date: Fri, 15 Dec 2006 17:46:41 +0000
Bugzilla: 218966
Message-Id: <1166204801.3752.1254.camel@quoit.chygwyn.com>
Changelog: gfs2: Use try locks in readpages


Hi,

This is the main part of the GFS2 fix for this particular bug. See
the initial message in the series for a full explanation.

This patch is taken from upstream. It uses "try locks" in readpages,
readpage and prepare_write in order to avoid a deadlock between glocks
the page lock.

Steve.

>From 2ca99501fa5422e84f18333918a503433449e2b5 Mon Sep 17 00:00:00 2001

This fixes a race between the glock and the page lock encountered
during truncate in gfs2_readpage and gfs2_prepare_write. The gfs2_readpages
function doesn't need the same fix since it only uses a try lock anyway, so
it will fail back to gfs2_readpage in the case of a potential deadlock.

This bug was spotted by Russell Cattelan.

Cc: Russell Cattelan <cattelan@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
---
 fs/gfs2/glock.h       |    1 -
 fs/gfs2/ops_address.c |   13 +++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h
index b985627..a331bf8 100644
--- a/fs/gfs2/glock.h
+++ b/fs/gfs2/glock.h
@@ -27,7 +27,6 @@
 #define GL_ATIME		0x00000200
 #define GL_NOCACHE		0x00000400
 #define GL_NOCANCEL		0x00001000
-#define GL_AOP			0x00004000
 #define GL_DUMP			0x00008000
 
 #define GLR_TRYFAILED		13
diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 5c3962c..3822189 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -230,7 +230,7 @@ static int gfs2_readpage(struct file *fi
 				/* gfs2_sharewrite_nopage has grabbed the ip->i_gl already */
 				goto skip_lock;
 		}
-		gfs2_holder_init(ip->i_gl, LM_ST_SHARED, GL_ATIME|GL_AOP, &gh);
+		gfs2_holder_init(ip->i_gl, LM_ST_SHARED, GL_ATIME|LM_FLAG_TRY_1CB, &gh);
 		do_unlock = 1;
 		error = gfs2_glock_nq_m_atime(1, &gh);
 		if (unlikely(error))
@@ -254,6 +254,8 @@ skip_lock:
 out:
 	return error;
 out_unlock:
+	if (error == GLR_TRYFAILED)
+		error = AOP_TRUNCATED_PAGE;
 	unlock_page(page);
 	if (do_unlock)
 		gfs2_holder_uninit(&gh);
@@ -293,7 +295,7 @@ static int gfs2_readpages(struct file *f
 				goto skip_lock;
 		}
 		gfs2_holder_init(ip->i_gl, LM_ST_SHARED,
-				 LM_FLAG_TRY_1CB|GL_ATIME|GL_AOP, &gh);
+				 LM_FLAG_TRY_1CB|GL_ATIME, &gh);
 		do_unlock = 1;
 		ret = gfs2_glock_nq_m_atime(1, &gh);
 		if (ret == GLR_TRYFAILED)
@@ -366,10 +368,13 @@ static int gfs2_prepare_write(struct fil
 	unsigned int write_len = to - from;
 
 
-	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ATIME|GL_AOP, &ip->i_gh);
+	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, GL_ATIME|LM_FLAG_TRY_1CB, &ip->i_gh);
 	error = gfs2_glock_nq_m_atime(1, &ip->i_gh);
-	if (error)
+	if (unlikely(error)) {
+		if (error == GLR_TRYFAILED)
+			error = AOP_TRUNCATED_PAGE;
 		goto out_uninit;
+	}
 
 	gfs2_write_calc_reserv(ip, write_len, &data_blocks, &ind_blocks);
 
-- 
1.4.1