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Re: [Linux-cluster] Freeze with cluster-2.03.11



On Sun, 5 Apr 2009, Wendy Cheng wrote:

> Based on code reading ...
> 1. iput() gets inode_lock (a spin lock)
> 2. iput() calls iput_final()
> 3. iput_final() calls gfs_drop_inode() that calls
>    generic_drop_inode()
> 4. generic_drop_inode() unlocks inode_lock.
> 
> In theory, this logic violates the usage of spin lock as it is expected 
> to lock for a short period of time but gfs_drop_inode() could take a 
> while to finish. It has a blocking write page that need to make sure the 
> data gets sync-ed to storage before it can returns. Make matter worse is 
> that inode_lock is a global lock that could block non-GFS threads. One 
> would think a quick fix is to drop the inode_lock at the beginning of 
> gfs_drop_inode() and then re-acquires it after gfs sync the page. 
> Unfortunately, inode_lock is not an exported symbol and GFS is an 
> out-of-tree filesystem that has to be compiled as a kernel module. So 
> this trick won't work for GFS.

Actually, it can work. inode_lock is not private and gfs can unlock/lock 
it:

--- gfs-orig/ops_super.c	2009-01-22 13:33:51.000000000 +0100
+++ gfs/ops_super.c	2009-04-06 13:07:06.000000000 +0200
@@ -9,6 +9,7 @@
 #include <linux/statfs.h>
 #include <linux/seq_file.h>
 #include <linux/mount.h>
+#include <linux/writeback.h>
 
 #include "gfs.h"
 #include "dio.h"
@@ -68,8 +69,11 @@
 	if (ip &&
 	    !inode->i_nlink &&
 	    S_ISREG(inode->i_mode) &&
-	    !sdp->sd_args.ar_localcaching)
+	    !sdp->sd_args.ar_localcaching) {
+	    	spin_unlock(&inode_lock);
 		gfs_sync_page_i(inode, DIO_START | DIO_WAIT);
+		spin_lock(&inode_lock);
+	}
 	generic_drop_inode(inode);
 }

Tomorrow I'll give it a try, there's no time to test it today.

> With a flight to catch tomorrow and a flu-infected body, I lose the will 
> to think over what the correct fix should and/or will be.

A speedy recover! And thank you all your efforts!

Best regards,
Jozsef
--
E-mail : kadlec mail kfki hu, kadlec blackhole kfki hu
PGP key: http://www.kfki.hu/~kadlec/pgp_public_key.txt
Address: KFKI Research Institute for Particle and Nuclear Physics
         H-1525 Budapest 114, POB. 49, Hungary


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