From: Josef Whiter <jwhiter@redhat.com>
Subject: [RHEL5.1] GFS2: Fix bz 229080, fix softlockups
Date: Thu, 8 Mar 2007 08:47:07 -0500
Bugzilla: 229080
Message-Id: <20070308134707.GC22561@korben.rdu.redhat.com>
Changelog: [gfs2] fix softlockups


Hello,

This patch depends on Steve's patch for bz 224686.  It has been submitted and
accepted upstream.  Thank you,

Josef


diff-tree fb5e727f62045204b376ad9ccde4fa40aa190946 (from 47443fa53289a841ff2b6aa6356df1f7e7b4f24b)
Author: Josef Whiter <jwhiter@redhat.com>

    [GFS2] fix hangup when multiple processes are trying to write to the same file
    
    This fixes a problem I encountered while running bonnie++.  When you have one
    thread that opens a file and starts to write to it, and then another thread that
    tries to open and write to the same file, the second thread will loop forever
    trying to grab the inode lock for that inode.  Basically we come in through
    generic_buffered_file_write, which calls gfs2_prepare_write, which then attempts
    to grab the glock.  Because we don't own the lock, gfs2_prepare_write gets
    GLR_TRYFAILED, which returns AOP_TRUNCATED_PAGE to generic_buffered_file_write.
    At this point generic_buffered_file_write loops around again and immediately
    retries the prepare_write.  This means that the second process never gets off of
    the processor in order to allow the process that holds the lock to finish its
    work and let go of the lock.  This patch makes gfs2_glock_nq schedule() if it
    gets back a GLR_TRYFAILED, which resolves this problem.
    
    Signed-off-by: Josef Whiter <jwhiter@redhat.com>
    Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
    

diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 56e3359..b3b7e84 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -266,9 +266,11 @@ skip_lock:
 out:
 	return error;
 out_unlock:
-	if (error == GLR_TRYFAILED)
-		error = AOP_TRUNCATED_PAGE;
 	unlock_page(page);
+	if (error == GLR_TRYFAILED) {
+		error = AOP_TRUNCATED_PAGE;
+		yield();
+	}
 	if (do_unlock)
 		gfs2_holder_uninit(&gh);
 	goto out;
@@ -364,6 +366,7 @@ static int gfs2_prepare_write(struct fil
 		if (error == GLR_TRYFAILED) {
 			unlock_page(page);
 			error = AOP_TRUNCATED_PAGE;
+			yield();
 		}
 		goto out_uninit;
 	}