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author | Vladimir Davydov <vdavydov@parallels.com> | 2014-04-03 14:48:21 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-04-03 16:21:04 -0700 |
commit | bcccff93af359533683603255124fc19eb12613d (patch) | |
tree | ccba7107fcb9b08fb038af3b90d0ee213cbe3757 /lib/kobject_uevent.c | |
parent | 5509a5d27b971a90b940e148ca9ca53312e4fa7a (diff) | |
download | op-kernel-dev-bcccff93af359533683603255124fc19eb12613d.zip op-kernel-dev-bcccff93af359533683603255124fc19eb12613d.tar.gz |
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>
Diffstat (limited to 'lib/kobject_uevent.c')
-rw-r--r-- | lib/kobject_uevent.c | 42 |
1 files changed, 36 insertions, 6 deletions
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c index 5f72767..4e3bd71 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: |