diff options
| -rw-r--r-- | kernel/kmod.c | 32 |
1 files changed, 24 insertions, 8 deletions
diff --git a/kernel/kmod.c b/kernel/kmod.c index d910b63..81c6705 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -225,8 +225,8 @@ static int call_usermodehelper_exec_async(void *data) spin_unlock_irq(¤t->sighand->siglock); /* - * Our parent is keventd, which runs with elevated scheduling priority. - * Avoid propagating that into the userspace child. + * Our parent is khelper which runs with elevated scheduling + * priority. Avoid propagating that into the userspace child. */ set_user_nice(current, 0); @@ -267,7 +267,11 @@ out: do_exit(0); } -/* Keventd can't block, but this (a child) can. */ +/* + * Handles UMH_WAIT_PROC. Our parent khelper can't wait for usermodehelper + * completion without blocking every other pending requests. That's why + * we use a kernel thread dedicated for that purpose. + */ static int call_usermodehelper_exec_sync(void *data) { struct subprocess_info *sub_info = data; @@ -283,8 +287,8 @@ static int call_usermodehelper_exec_sync(void *data) /* * Normally it is bogus to call wait4() from in-kernel because * wait4() wants to write the exit code to a userspace address. - * But call_usermodehelper_exec_sync() always runs as keventd, - * and put_user() to a kernel address works OK for kernel + * But call_usermodehelper_exec_sync() always runs as kernel + * thread and put_user() to a kernel address works OK for kernel * threads, due to their having an mm_segment_t which spans the * entire address space. * @@ -305,7 +309,19 @@ static int call_usermodehelper_exec_sync(void *data) do_exit(0); } -/* This is run by khelper thread */ +/* + * This function doesn't strictly needs to be called asynchronously. But we + * need to create the usermodehelper kernel threads from a task that is affine + * to all CPUs (or nohz housekeeping ones) such that they inherit a widest + * affinity irrespective of call_usermodehelper() callers with possibly reduced + * affinity (eg: per-cpu workqueues). We don't want usermodehelper targets to + * contend any busy CPU. + * Khelper provides such wide affinity. + * + * Besides, khelper provides the privilege level that caller might not have to + * perform the usermodehelper request. + * + */ static void call_usermodehelper_exec_work(struct work_struct *work) { struct subprocess_info *sub_info = @@ -533,8 +549,8 @@ EXPORT_SYMBOL(call_usermodehelper_setup); * from interrupt context. * * Runs a user-space application. The application is started - * asynchronously if wait is not set, and runs as a child of keventd. - * (ie. it runs with full root capabilities). + * asynchronously if wait is not set, and runs as a child of khelper. + * (ie. it runs with full root capabilities and wide affinity). */ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) { |
