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Commit d0bd587a authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

usermodehelper: implement UMH_KILLABLE 



Implement UMH_KILLABLE, should be used along with UMH_WAIT_EXEC/PROC.
The caller must ensure that subprocess_info->path/etc can not go away
until call_usermodehelper_freeinfo().

call_usermodehelper_exec(UMH_KILLABLE) does
wait_for_completion_killable.  If it fails, it uses
xchg(&sub_info->complete, NULL) to serialize with umh_complete() which
does the same xhcg() to access sub_info->complete.

If call_usermodehelper_exec wins, it can safely return.  umh_complete()
should get NULL and call call_usermodehelper_freeinfo().

Otherwise we know that umh_complete() was already called, in this case
call_usermodehelper_exec() falls back to wait_for_completion() which
should succeed "very soon".

Note: UMH_NO_WAIT == -1 but it obviously should not be used with
UMH_KILLABLE.  We delay the neccessary cleanup to simplify the back
porting.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Tejun Heo <tj@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b3449922

include/linux/kmod.h

+2 −0
Original line number Diff line number Diff line
@@ -54,6 +54,8 @@ enum umh_wait { 
	UMH_WAIT_PROC = 1,	/* wait for the process to complete */

};



#define UMH_KILLABLE	4	/* wait for EXEC/PROC killable */



struct subprocess_info {

	struct work_struct work;

	struct completion *complete;

kernel/kmod.c

+25 −2
Original line number Diff line number Diff line
@@ -201,7 +201,15 @@ EXPORT_SYMBOL(call_usermodehelper_freeinfo); 


static void umh_complete(struct subprocess_info *sub_info)

{

	complete(sub_info->complete);

	struct completion *comp = xchg(&sub_info->complete, NULL);

	/*

	 * See call_usermodehelper_exec(). If xchg() returns NULL

	 * we own sub_info, the UMH_KILLABLE caller has gone away.

	 */

	if (comp)

		complete(comp);

	else

		call_usermodehelper_freeinfo(sub_info);

}



/* Keventd can't block, but this (a child) can. */
@@ -252,6 +260,9 @@ static void __call_usermodehelper(struct work_struct *work) 
	enum umh_wait wait = sub_info->wait;

	pid_t pid;



	if (wait != UMH_NO_WAIT)

		wait &= ~UMH_KILLABLE;



	/* CLONE_VFORK: wait until the usermode helper has execve'd

	 * successfully We need the data structures to stay around

	 * until that is done.  */
@@ -461,9 +472,21 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, 
	queue_work(khelper_wq, &sub_info->work);

	if (wait == UMH_NO_WAIT)	/* task has freed sub_info */

		goto unlock;



	if (wait & UMH_KILLABLE) {

		retval = wait_for_completion_killable(&done);

		if (!retval)

			goto wait_done;



		/* umh_complete() will see NULL and free sub_info */

		if (xchg(&sub_info->complete, NULL))

			goto unlock;

		/* fallthrough, umh_complete() was already called */

	}



	wait_for_completion(&done);

wait_done:

	retval = sub_info->retval;



out:

	call_usermodehelper_freeinfo(sub_info);

unlock: