Home » Mailing list archives » linux-kernel » 2007 » November » 1

[PATCH 21/27] r-o-bind-mounts-make-access-use-mnt-check

!MAILaRCHIVE_VOTE_RePLACE
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
[view in full thread]
From: Dave Hansen <haveblue@...>
To: <akpm@...>
Cc: <linux-kernel@...>, <miklos@...>, <hch@...>, Dave Hansen <haveblue@...>
Subject: [PATCH 21/27] r-o-bind-mounts-make-access-use-mnt-check
Date: Thursday, November 1, 2007 - 7:08 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.

Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 linux-2.6.git-dave/fs/open.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff -puN fs/open.c~r-o-bind-mounts-make-access-use-mnt-check fs/open.c
--- linux-2.6.git/fs/open.c~r-o-bind-mounts-make-access-use-mnt-check	2007-11-01 14:46:18.000000000 -0700
+++ linux-2.6.git-dave/fs/open.c	2007-11-01 14:46:18.000000000 -0700
@@ -459,8 +459,17 @@ 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:
_
-
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
Messages in current thread:
[PATCH 00/27] Read-only bind mounts (-mm resend), Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 27/27] keep track of mnt_writer state of struct file, Dave Hansen, (Thu Nov 1, 7:09 pm)
[PATCH 25/27] r-o-bind-mounts-track-number-of-mount-writers-..., Dave Hansen, (Thu Nov 1, 7:09 pm)
Re: [PATCH 25/27] r-o-bind-mounts-track-number-of-mount-writ..., Andrew Morton, (Mon Nov 5, 7:35 pm)
[PATCH 22/27] r-o-bind-mounts-nfs-check-mnt-instead-of-super..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 24/27] r-o-bind-mounts-track-number-of-mount-writers, Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 26/27] r-o-bind-mounts-honor-r-w-changes-at-do_remoun..., Dave Hansen, (Thu Nov 1, 7:09 pm)
[PATCH 19/27] r-o-bind-mounts-elevate-writer-count-for-chown..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 23/27] r-o-bind-mounts-sys_mknodat-elevate-write-coun..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 18/27] r-o-bind-mounts-elevate-write-count-over-calls..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 21/27] r-o-bind-mounts-make-access-use-mnt-check, Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 20/27] r-o-bind-mounts-elevate-writer-count-for-do_sy..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 17/27] r-o-bind-mounts-elevate-write-count-opend-files, Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 16/27] r-o-bind-mounts-elevate-write-count-for-some-i..., Dave Hansen, (Thu Nov 1, 7:08 pm)
Re: [PATCH 16/27] r-o-bind-mounts-elevate-write-count-for-so..., Andrew Morton, (Mon Nov 5, 7:23 pm)
Re: [PATCH 16/27] r-o-bind-mounts-elevate-write-count-for-so..., Jan Kara, (Tue Nov 6, 5:01 am)
Re: [PATCH 16/27] r-o-bind-mounts-elevate-write-count-for-so..., Andrew Morton, (Tue Nov 6, 5:12 am)
[PATCH 13/27] r-o-bind-mounts-elevate-write-count-for-do_uti..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 15/27] r-o-bind-mounts-elevate-write-count-for-link-a..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 12/27] r-o-bind-mounts-elevate-write-count-for-do_sys..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 11/27] r-o-bind-mounts-elevate-write-count-during-ent..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 14/27] r-o-bind-mounts-elevate-write-count-for-file_u..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 07/27] r-o-bind-mounts-do_rmdir-elevate-write-count, Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 10/27] r-o-bind-mounts-elevate-mount-count-for-extend..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 01/27] do namei_flags calculation inside open_namei(), Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 09/27] r-o-bind-mounts-elevate-mnt-writers-for-vfs_un..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 06/27] r-o-bind-mounts-stub-functions, Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 08/27] r-o-bind-mounts-elevate-mnt-writers-for-caller..., Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 05/27] rename open_namei() to open_pathname(), Dave Hansen, (Thu Nov 1, 7:08 pm)
Re: [PATCH 05/27] rename open_namei() to open_pathname(), Christoph Hellwig, (Mon Nov 26, 10:33 am)
[PATCH 04/27] kill filp_open(), Dave Hansen, (Thu Nov 1, 7:08 pm)
Re: [PATCH 04/27] kill filp_open(), Andrew Morton, (Wed Jan 16, 4:52 am)
Re: [PATCH 04/27] kill filp_open(), Dave Hansen, (Wed Jan 16, 1:04 pm)
Re: [PATCH 04/27] kill filp_open(), Bryn M. Reeves, (Wed Jan 16, 1:12 pm)
Re: [PATCH 04/27] kill filp_open(), Christoph Hellwig, (Wed Jan 16, 1:10 pm)
Re: [PATCH 04/27] kill filp_open(), Dave Hansen, (Wed Jan 16, 1:41 pm)
Re: [PATCH 04/27] kill filp_open(), Christoph Hellwig, (Wed Jan 16, 1:47 pm)
[PATCH 03/27] kill do_filp_open(), Dave Hansen, (Thu Nov 1, 7:08 pm)
[PATCH 02/27] make open_namei() return a filp, Dave Hansen, (Thu Nov 1, 7:08 pm)