linux-kernel - [BUG][PATCH -mm] avoid BUG() in __stop_machine

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Date:	Thu, 19 Jun 2008 15:59:50 +0900
From:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, kernel-testers@...r.kernel.org,
	linux-mm@...ck.org, sugita <yumiko.sugita.yf@...achi.com>,
	Satoshi OSHIMA <satoshi.oshima.fk@...achi.com>,
	rusty@...tcorp.com.au
Subject: [BUG][PATCH -mm] avoid BUG() in __stop_machine_run()

When a process loads a kernel module, __stop_machine_run() is called, and
it calls sched_setscheduler() to give newly created kernel threads highest
priority.  However, the process can have no CAP_SYS_NICE which required
for sched_setscheduler() to increase the priority.  For example, SystemTap
loads its module with only CAP_SYS_MODULE.  In this case,
sched_setscheduler() returns -EPERM, then BUG() is called.

Failure of sched_setscheduler() wouldn't be a real problem, so this
patch just ignores it.
Or, should we give the CAP_SYS_NICE capability temporarily?

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
---
 kernel/stop_machine.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Index: linux-2.6.26-rc5-mm3/kernel/stop_machine.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/kernel/stop_machine.c
+++ linux-2.6.26-rc5-mm3/kernel/stop_machine.c
@@ -143,8 +143,7 @@ int __stop_machine_run(int (*fn)(void *)
 		kthread_bind(threads[i], i);

 		/* Make it highest prio. */
-		if (sched_setscheduler(threads[i], SCHED_FIFO, &param) != 0)
-			BUG();
+		sched_setscheduler(threads[i], SCHED_FIFO, &param);
 	}

 	/* We've created all the threads.  Wake them all: hold this CPU so one

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