linux-kernel - Re: [PATCH] x86: endless page faults in mount_block

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Message-ID: <20080429143314.GG26461@elte.hu>
Date:	Tue, 29 Apr 2008 16:33:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Henry Nestler <Henry.Ne@...or.de>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@....linux.org.uk>
Subject: Re: [PATCH] x86: endless page faults in mount_block_root for Linux
	2.6


* Henry Nestler <Henry.Ne@...or.de> wrote:

> I'm not shure with the VFS fix. The change only has effect for x86 and 
> x86_64. I'm afraid. Mostly other architectures no need to change. I 
> would only public the base of the problem. Perhaps no need to change 
> here.

btw., i have a kmemcheck-reported bug fixed in this same area with the 
patch below. I dont remember the details anymore, but the root mount 
code did something really, really weird here.

	Ingo

------------>
Subject: init: root mount fix
From: Ingo Molnar <mingo@...e.hu>
Date: Tue Apr 29 16:31:50 CEST 2008

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 init/do_mounts.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux/init/do_mounts.c
===================================================================
--- linux.orig/init/do_mounts.c
+++ linux/init/do_mounts.c
@@ -201,9 +201,13 @@ static int __init do_mount_root(char *na
 	return 0;
 }
 
+#if PAGE_SIZE < PATH_MAX
+# error increase the fs_names allocation size here
+#endif
+
 void __init mount_block_root(char *name, int flags)
 {
-	char *fs_names = __getname();
+	char *fs_names = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, 1);
 	char *p;
 #ifdef CONFIG_BLOCK
 	char b[BDEVNAME_SIZE];
@@ -251,7 +255,7 @@ retry:
 #endif
 	panic("VFS: Unable to mount root fs on %s", b);
 out:
-	putname(fs_names);
+	free_pages((unsigned long)fs_names, 1);
 }
  
 #ifdef CONFIG_ROOT_NFS
--
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