Commit 303d379c authored Apr 02, 2009 by Yasunori Goto Committed by Linus Torvalds Apr 02, 2009

hpet: fix the possibility of insane return value of hpet_calibrate() against SMI



hpet_calibrate() has a possibility of miss-calibration due to SMI.  If SMI
interrupts in the while loop of calibration, then return value will be
big.  This change calibrates until stabilizing by the return value with a
small value.

[akpm@linux-foundation.org: trivial style tweaks]
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Acked-by: Vojtech Pavlik <vojtech@suse.cz>
Cc: Robert Picco <Robert.Picco@hp.com>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 1f80769f

drivers/char/hpet.c

+21 −1

Original line number	Diff line number	Diff line
		@@ -713,7 +713,7 @@ static struct ctl_table_header *sysctl_header;
		*/
		#define TICK_CALIBRATE (1000UL)

		static unsigned long hpet_calibrate(struct hpets *hpetp)
		static unsigned long __hpet_calibrate(struct hpets *hpetp)
		{
		struct hpet_timer __iomem *timer = NULL;
		unsigned long t, m, count, i, flags, start;
		@@ -750,6 +750,26 @@ static unsigned long hpet_calibrate(struct hpets *hpetp)
		return (m - start) / i;
		}

		static unsigned long hpet_calibrate(struct hpets *hpetp)
		{
		unsigned long ret = -1;
		unsigned long tmp;

		/*
		* Try to calibrate until return value becomes stable small value.
		* If SMI interruption occurs in calibration loop, the return value
		* will be big. This avoids its impact.
		*/
		for ( ; ; ) {
		tmp = __hpet_calibrate(hpetp);
		if (ret <= tmp)
		break;
		ret = tmp;
		}

		return ret;
		}

		int hpet_alloc(struct hpet_data *hdp)
		{
		u64 cap, mcfg;

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