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authorVladimir Davydov <vdavydov@parallels.com>2014-04-04 01:48:21 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2014-04-04 03:21:04 +0400
commitbcccff93af359533683603255124fc19eb12613d (patch)
treeccba7107fcb9b08fb038af3b90d0ee213cbe3757
parent5509a5d27b971a90b940e148ca9ca53312e4fa7a (diff)
downloadlinux-bcccff93af359533683603255124fc19eb12613d.tar.xz
kobject: don't block for each kobject_uevent
Currently kobject_uevent has somewhat unpredictable semantics. The point is, since it may call a usermode helper and wait for it to execute (UMH_WAIT_EXEC), it is impossible to say for sure what lock dependencies it will introduce for the caller - strictly speaking it depends on what fs the binary is located on and the set of locks fork may take. There are quite a few kobject_uevent's users that do not take this into account and call it with various mutexes taken, e.g. rtnl_mutex, net_mutex, which might potentially lead to a deadlock. Since there is actually no reason to wait for the usermode helper to execute there, let's make kobject_uevent start the helper asynchronously with the aid of the UMH_NO_WAIT flag. Personally, I'm interested in this, because I really want kobject_uevent to be called under the slab_mutex in the slub implementation as it used to be some time ago, because it greatly simplifies synchronization and automatically fixes a kmemcg-related race. However, there was a deadlock detected on an attempt to call kobject_uevent under the slab_mutex (see https://lkml.org/lkml/2012/1/14/45), which was reported to be fixed by releasing the slab_mutex for kobject_uevent. Unfortunately, there was no information about who exactly blocked on the slab_mutex causing the usermode helper to stall, neither have I managed to find this out or reproduce the issue. BTW, this is not the first attempt to make kobject_uevent use UMH_NO_WAIT. Previous one was made by commit f520360d93cd ("kobject: don't block for each kobject_uevent"), but it was wrong (it passed arguments allocated on stack to async thread) so it was reverted in 05f54c13cd0c ("Revert "kobject: don't block for each kobject_uevent"."). It targeted on speeding up the boot process though. Signed-off-by: Vladimir Davydov <vdavydov@parallels.com> Cc: Greg KH <greg@kroah.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/kobject.h1
-rw-r--r--lib/kobject_uevent.c42
2 files changed, 37 insertions, 6 deletions
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 926afb6f6b5f..f896a33e8341 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -119,6 +119,7 @@ struct kobj_type {
};
struct kobj_uevent_env {
+ char *argv[3];
char *envp[UEVENT_NUM_ENVP];
int envp_idx;
char buf[UEVENT_BUFFER_SIZE];
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 5f72767ddd9b..4e3bd71bd949 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -124,6 +124,30 @@ static int kobj_usermode_filter(struct kobject *kobj)
return 0;
}
+static int init_uevent_argv(struct kobj_uevent_env *env, const char *subsystem)
+{
+ int len;
+
+ len = strlcpy(&env->buf[env->buflen], subsystem,
+ sizeof(env->buf) - env->buflen);
+ if (len >= (sizeof(env->buf) - env->buflen)) {
+ WARN(1, KERN_ERR "init_uevent_argv: buffer size too small\n");
+ return -ENOMEM;
+ }
+
+ env->argv[0] = uevent_helper;
+ env->argv[1] = &env->buf[env->buflen];
+ env->argv[2] = NULL;
+
+ env->buflen += len + 1;
+ return 0;
+}
+
+static void cleanup_uevent_env(struct subprocess_info *info)
+{
+ kfree(info->data);
+}
+
/**
* kobject_uevent_env - send an uevent with environmental data
*
@@ -301,11 +325,8 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
/* call uevent_helper, usually only enabled during early boot */
if (uevent_helper[0] && !kobj_usermode_filter(kobj)) {
- char *argv [3];
+ struct subprocess_info *info;
- argv [0] = uevent_helper;
- argv [1] = (char *)subsystem;
- argv [2] = NULL;
retval = add_uevent_var(env, "HOME=/");
if (retval)
goto exit;
@@ -313,9 +334,18 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
"PATH=/sbin:/bin:/usr/sbin:/usr/bin");
if (retval)
goto exit;
+ retval = init_uevent_argv(env, subsystem);
+ if (retval)
+ goto exit;
- retval = call_usermodehelper(argv[0], argv,
- env->envp, UMH_WAIT_EXEC);
+ retval = -ENOMEM;
+ info = call_usermodehelper_setup(env->argv[0], env->argv,
+ env->envp, GFP_KERNEL,
+ NULL, cleanup_uevent_env, env);
+ if (info) {
+ retval = call_usermodehelper_exec(info, UMH_NO_WAIT);
+ env = NULL; /* freed by cleanup_uevent_env */
+ }
}
exit: