linux-kernel - [PATCH 06/26] sysfs: Don't hold addrm_start/addrm

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Date:	Fri, 29 May 2009 13:19:16 -0700
From:	"Eric W. Biederman" <ebiederm@...ssion.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Cc:	<linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	<linux-fsdevel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>, Greg KH <greg@...ah.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: [PATCH 06/26] sysfs: Don't hold addrm_start/addrm_finish over multiple removals.

From: Eric W. Biederman <ebiederm@...ssion.com>

With respect to the basic integrity of the sysfs data structures holding
the locks across the deletion of multiple sysfs_dirents is unnecessary.

Upper layers are required to coordinate their activity so that they
do not add or delete entries in sysfs directories as they are being
removed, and I have seen nothing to indicate the don't. The upper layers
can not rely on sysfs doing anything for them as it is a compile option
and may not be there.  So the previous atomic delete of the directory
entries and the directory serves no useful purpose.

By removing the only case where addrm_start/addrm_finish are held
over multiple dirent removals I simplify the requirements and
pave the way removing sysfs_addrm_start and sysfs_addrm_finish
completely.

Additionally add some comments explaining some of the thinking behind
sysfs_dirent removal in __sysfs_remove_dir.

Signed-off-by: Eric W. Biederman <ebiederm@...stanetworks.com>
---
 fs/sysfs/dir.c |   36 +++++++++++++++++++++++++-----------
 1 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 60482be..3e3a87f 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -762,23 +762,37 @@ void sysfs_remove_subdir(struct sysfs_dirent *sd)
 	remove_dir(sd);
 }
 
+static struct sysfs_dirent *get_dirent_to_remove(struct sysfs_dirent *dir_sd)
+{
+	struct sysfs_dirent *sd;
+
+	mutex_lock(&sysfs_mutex);
+	for (sd = dir_sd->s_dir.children; sd; sd = sd->s_sibling) {
+		/* Directories might be owned by someone else
+		 * making recursive directory removal unsafe.
+		 */
+		if (sysfs_type(sd) == SYSFS_DIR)
+			continue;
+		break;
+	}
+	sysfs_get(sd);
+	mutex_unlock(&sysfs_mutex);
+
+	return sd;
+}
 
 static void __sysfs_remove_dir(struct sysfs_dirent *dir_sd)
 {
 	struct sysfs_addrm_cxt acxt;
-	struct sysfs_dirent **pos;
-
-	sysfs_addrm_start(&acxt, dir_sd);
-	pos = &dir_sd->s_dir.children;
-	while (*pos) {
-		struct sysfs_dirent *sd = *pos;
+	struct sysfs_dirent *sd;
 
-		if (sysfs_type(sd) != SYSFS_DIR)
-			sysfs_remove_one(&acxt, sd);
-		else
-			pos = &(*pos)->s_sibling;
+	/* Remove children that we think are safe */
+	while ((sd = get_dirent_to_remove(dir_sd))) {
+		sysfs_addrm_start(&acxt, sd->s_parent);
+		sysfs_remove_one(&acxt, sd);
+		sysfs_addrm_finish(&acxt);
+		sysfs_put(sd);
 	}
-	sysfs_addrm_finish(&acxt);
 
 	remove_dir(dir_sd);
 }
-- 
1.6.3.1.54.g99dd.dirty

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