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Subject[PATCH 06/26] sysfs: Don't hold addrm_start/addrm_finish over multiple removals.
From: Eric W. Biederman <ebiederm@xmission.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@aristanetworks.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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