Subject: [merged] kobject-dont-block-for-each-kobject_uevent.patch removed from -mm tree To: vdavydov@xxxxxxxxxxxxx,cl@xxxxxxxxx,greg@xxxxxxxxx,penberg@xxxxxxxxxx,mm-commits@xxxxxxxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Fri, 04 Apr 2014 12:32:12 -0700 The patch titled Subject: kobject: don't block for each kobject_uevent has been removed from the -mm tree. Its filename was kobject-dont-block-for-each-kobject_uevent.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx> Subject: 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 f520360d93c ("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@xxxxxxxxxxxxx> Cc: Greg KH <greg@xxxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/kobject.h | 1 lib/kobject_uevent.c | 42 ++++++++++++++++++++++++++++++++------ 2 files changed, 37 insertions(+), 6 deletions(-) diff -puN include/linux/kobject.h~kobject-dont-block-for-each-kobject_uevent include/linux/kobject.h --- a/include/linux/kobject.h~kobject-dont-block-for-each-kobject_uevent +++ a/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 -puN lib/kobject_uevent.c~kobject-dont-block-for-each-kobject_uevent lib/kobject_uevent.c --- a/lib/kobject_uevent.c~kobject-dont-block-for-each-kobject_uevent +++ a/lib/kobject_uevent.c @@ -124,6 +124,30 @@ static int kobj_usermode_filter(struct k 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 *k /* 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 *k "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: _ Patches currently in -mm which might be from vdavydov@xxxxxxxxxxxxx are origin.patch linux-next.patch memcg-slab-never-try-to-merge-memcg-caches.patch memcg-slab-cleanup-memcg-cache-creation.patch memcg-slab-separate-memcg-vs-root-cache-creation-paths.patch memcg-slab-unregister-cache-from-memcg-before-starting-to-destroy-it.patch memcg-slab-do-not-destroy-children-caches-if-parent-has-aliases.patch slub-adjust-memcg-caches-when-creating-cache-alias.patch slub-rework-sysfs-layout-for-memcg-caches.patch slub-fix-leak-of-name-in-sysfs_slab_add.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html