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

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Date:	Tue, 29 Apr 2008 18:14:33 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Henry Nestler" <Henry.Ne@...or.de>, 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>,
	"Vegard Nossum" <vegard.nossum@...il.com>
Subject: Re: [PATCH] x86: endless page faults in mount_block_root for Linux 2.6

On Tue, Apr 29, 2008 at 5:33 PM, Ingo Molnar <mingo@...e.hu> wrote:
>  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.
>
>  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

It could have been a bug in early kmemcheck too. We don't check memory
allocated with the page allocator, only slab, so this shouldn't
trigger anything.
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