Commit 15075897 authored Dec 23, 2013 by Michael Ellerman Committed by Benjamin Herrenschmidt Feb 11, 2014

powerpc/xmon: Fix timeout loop in get_output_lock()



As far as I can tell, our 70s era timeout loop in get_output_lock() is
generating no code.

This leads to the hostile takeover happening more or less simultaneously
on all cpus. The result is "interesting", some example output that is
more readable than most:

    cpu 0x1: Vector: 100 (Scypsut e0mx bR:e setV)e catto xc0p:u[ c 00
    c0:0  000t0o0V0erc0td:o5 rfc28050000]0c00 0 0  0 6t(pSrycsV1ppuot
    uxe 1m 2 0Rx21e3:0s0ce000c00000t00)00 60602oV2SerucSayt0y 0p 1sxs

Fix it by using udelay() in the timeout loop. The wait time and check
frequency are arbitrary, but seem to work OK. We already rely on
udelay() working so this is not a new dependency.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

parent 730efb61

arch/powerpc/xmon/xmon.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -315,10 +315,17 @@ static void get_output_lock(void)
		if (last_speaker == 0)
		return;

		timeout = 10000000;
		/*
		* Wait a full second for the lock, we might be on a slow
		* console, but check every 100us.
		*/
		timeout = 10000;
		while (xmon_speaker == last_speaker) {
		if (--timeout > 0)
		if (--timeout > 0) {
		udelay(100);
		continue;
		}

		/* hostile takeover */
		prev = cmpxchg(&xmon_speaker, last_speaker, me);
		if (prev == last_speaker)

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