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[PATCH 08/24] make access() use mnt check

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From: Dave Hansen <haveblue@...>
To: <akpm@...>
Cc: <linux-kernel@...>, <hch@...>, Dave Hansen <haveblue@...>
Subject: [PATCH 08/24] make access() use mnt check
Date: Monday, September 17, 2007 - 2:27 pm

It is OK to let access() go without using a mnt_want/drop_write()
pair because it doesn't actually do writes to the filesystem,
and it is inherently racy anyway.  This is a rare case when it is
OK to use __mnt_is_readonly() directly.

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
---

 lxc-dave/fs/open.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff -puN fs/open.c~make-access-use-helper fs/open.c
--- lxc/fs/open.c~make-access-use-helper	2007-09-17 09:44:00.000000000 -0700
+++ lxc-dave/fs/open.c	2007-09-17 09:44:00.000000000 -0700
@@ -457,8 +457,17 @@ asmlinkage long sys_faccessat(int dfd, c
 	if(res || !(mode & S_IWOTH) ||
 	   special_file(nd.dentry->d_inode->i_mode))
 		goto out_path_release;
-
-	if(IS_RDONLY(nd.dentry->d_inode))
+	/*
+	 * This is a rare case where using __mnt_is_readonly()
+	 * is OK without a mnt_want/drop_write() pair.  Since
+	 * no actual write to the fs is performed here, we do
+	 * not need to telegraph to that to anyone.
+	 *
+	 * By doing this, we accept that this access is
+	 * inherently racy and know that the fs may change
+	 * state before we even see this result.
+	 */
+	if (__mnt_is_readonly(nd.mnt))
 		res = -EROFS;
 
 out_path_release:
_
-
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Messages in current thread:
[PATCH 00/24] Read-only bind mounts, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 00/24] Read-only bind mounts, Christoph Hellwig, (Wed Sep 19, 1:44 pm)
Re: [PATCH 00/24] Read-only bind mounts, Andrew Morton, (Wed Sep 19, 5:24 pm)
Re: [PATCH 00/24] Read-only bind mounts, Dave Hansen, (Wed Sep 19, 5:56 pm)
Re: [PATCH 00/24] Read-only bind mounts, Andrew Morton, (Wed Sep 19, 6:06 pm)
Re: [PATCH 00/24] Read-only bind mounts, Miklos Szeredi, (Thu Sep 20, 5:58 am)
Re: [PATCH 00/24] Read-only bind mounts, Serge E. Hallyn, (Wed Sep 19, 10:21 am)
[PATCH 14/24] unix_find_other() elevate write count for touc..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 14/24] unix_find_other() elevate write count for ..., Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 22/24] do_rmdir(): elevate write count, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 22/24] do_rmdir(): elevate write count, Christoph Hellwig, (Wed Sep 19, 1:39 pm)
[PATCH 21/24] elevate mnt writers for vfs_unlink() callers, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 21/24] elevate mnt writers for vfs_unlink() callers, Christoph Hellwig, (Wed Sep 19, 1:38 pm)
[PATCH 19/24] elevate write count for do_sys_utime() and tou..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 19/24] elevate write count for do_sys_utime() and..., Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 20/24] sys_mknodat(): elevate write count for vfs_mkn..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 20/24] sys_mknodat(): elevate write count for vfs..., Christoph Hellwig, (Wed Sep 19, 1:38 pm)
[PATCH 09/24] elevate mnt writers for callers of vfs_mkdir(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 09/24] elevate mnt writers for callers of vfs_mkd..., Christoph Hellwig, (Wed Sep 19, 1:32 pm)
[PATCH 04/24] r/o bind mounts: stub functions, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 04/24] r/o bind mounts: stub functions, Christoph Hellwig, (Wed Sep 19, 1:28 pm)
[PATCH 11/24] elevate write count for link and symlink calls, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 11/24] elevate write count for link and symlink c..., Christoph Hellwig, (Wed Sep 19, 1:33 pm)
[PATCH 06/24] r/o bind mounts: elevate write count for some ..., Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 06/24] r/o bind mounts: elevate write count for s..., Christoph Hellwig, (Wed Sep 19, 1:31 pm)
[PATCH 18/24] elevate write count for do_utimes(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 18/24] elevate write count for do_utimes(), Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 16/24] nfs: check mnt instead of superblock directly, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 16/24] nfs: check mnt instead of superblock direc..., Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 17/24] elevate writer count for do_sys_truncate(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 17/24] elevate writer count for do_sys_truncate(), Christoph Hellwig, (Wed Sep 19, 1:36 pm)
[PATCH 15/24] elevate write count over calls to vfs_rename(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 15/24] elevate write count over calls to vfs_rena..., Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 12/24] elevate mount count for extended attributes, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 12/24] elevate mount count for extended attributes, Christoph Hellwig, (Wed Sep 19, 1:34 pm)
[PATCH 10/24] elevate write count during entire ncp_ioctl(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 10/24] elevate write count during entire ncp_ioct..., Christoph Hellwig, (Wed Sep 19, 1:33 pm)
[PATCH 01/24] filesystem helpers for custom 'struct file's, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 01/24] filesystem helpers for custom 'struct file's, Christoph Hellwig, (Wed Sep 19, 1:26 pm)
[PATCH] docuement filesystem helpers for custom 'struct file's, Dave Hansen, (Wed Sep 19, 1:47 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Randy Dunlap, (Wed Sep 19, 6:07 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Dave Hansen, (Thu Sep 20, 1:25 pm)
Re: [PATCH] docuement filesystem helpers for custom 'struct ..., Christoph Hellwig, (Thu Sep 20, 1:30 pm)
[PATCH 05/24] elevate write count open()'d files, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 05/24] elevate write count open()'d files, Christoph Hellwig, (Wed Sep 19, 1:30 pm)
[PATCH 07/24] elevate writer count for chown and friends, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 07/24] elevate writer count for chown and friends, Christoph Hellwig, (Wed Sep 19, 1:31 pm)
[PATCH 13/24] elevate write count for file_update_time(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 13/24] elevate write count for file_update_time(), Christoph Hellwig, (Wed Sep 19, 1:35 pm)
[PATCH 08/24] make access() use mnt check, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 08/24] make access() use mnt check, Christoph Hellwig, (Wed Sep 19, 1:32 pm)
[PATCH 03/24] create cleanup helper svc_msnfs(), Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Jan Engelhardt, (Wed Sep 19, 1:39 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Dave Hansen, (Wed Sep 19, 1:45 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Trond Myklebust, (Wed Sep 19, 1:54 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Christoph Hellwig, (Wed Sep 19, 1:59 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Trond Myklebust, (Wed Sep 19, 2:10 pm)
Re: [PATCH 03/24] create cleanup helper svc_msnfs(), Christoph Hellwig, (Wed Sep 19, 1:28 pm)
[PATCH 02/24] rearrange may_open() to be r/o friendly, Dave Hansen, (Mon Sep 17, 2:27 pm)
Re: [PATCH 02/24] rearrange may_open() to be r/o friendly, Christoph Hellwig, (Wed Sep 19, 1:27 pm)
Re: [PATCH 02/24] rearrange may_open() to be r/o friendly, Dave Hansen, (Thu Sep 20, 2:47 pm)