usermodehelper: implement UMH_KILLABLE (d0bd587a) · Commits · 戴 / test

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:

Oleg 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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:

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