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Fix for longrun.c for degenerate case

PATCH H. Peter Anvin 2 participants 2 messages May 8, 2004 – May 9, 2004

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H. Peter Anvin

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#0 lore raw

Hi all,

I ran into a system the other day which had a Transmeta processor, but configured in a degenerate, fixed-frequency configuration. It crashed booting Fedora Core 2 test 3 due to a division by zero in the longrun cpufreq driver. The attached patch fixes this.

-hpa

Index: linux-2.5/arch/i386/kernel/cpu/cpufreq/longrun.c
===================================================================
RCS file: /home/hpa/kernel/bkcvs/linux-2.5/arch/i386/kernel/cpu/cpufreq/longrun.c,v retrieving revision 1.19

arch/i386/kernel/cpu/cpufreq/longrun.c +19 -9
diff -u -r1.19 longrun.c
@@ -46,11 +46,16 @@
 	rdmsr(MSR_TMTA_LONGRUN_CTRL, msr_lo, msr_hi);
 	msr_lo &= 0x0000007F;
 	msr_hi &= 0x0000007F;
-
-	policy->min = longrun_low_freq + msr_lo * 
-		((longrun_high_freq - longrun_low_freq) / 100);
-	policy->max = longrun_low_freq + msr_hi * 
-		((longrun_high_freq - longrun_low_freq) / 100);
+	
+	if ( longrun_high_freq <= longrun_low_freq ) {
+		/* Assume degenerate Longrun table */
+		policy->min = policy->max = longrun_high_freq;
+	} else {
+		policy->min = longrun_low_freq + msr_lo * 
+			((longrun_high_freq - longrun_low_freq) / 100);
+		policy->max = longrun_low_freq + msr_hi * 
+			((longrun_high_freq - longrun_low_freq) / 100);
+	}
 	policy->cpu = 0;
 }
 

@@ -70,10 +75,15 @@
 	if (!policy)
 		return -EINVAL;
 
-	pctg_lo = (policy->min - longrun_low_freq) / 
-		((longrun_high_freq - longrun_low_freq) / 100);
-	pctg_hi = (policy->max - longrun_low_freq) / 
-		((longrun_high_freq - longrun_low_freq) / 100);
+	if ( longrun_high_freq <= longrun_low_freq ) {
+		/* Assume degenerate Longrun table */
+		pctg_lo = pctg_hi = 100;
+	} else {
+		pctg_lo = (policy->min - longrun_low_freq) / 
+			((longrun_high_freq - longrun_low_freq) / 100);
+		pctg_hi = (policy->max - longrun_low_freq) / 
+			((longrun_high_freq - longrun_low_freq) / 100);
+	}
 
 	if (pctg_hi > 100)
 		pctg_hi = 100;

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#1 lore raw
Quoted 6 lines · H. Peter Anvin

Hi all,

I ran into a system the other day which had a Transmeta processor, but configured in a degenerate, fixed-frequency configuration. It crashed booting Fedora Core 2 test 3 due to a division by zero in the longrun cpufreq driver. The attached patch fixes this.

Thanks. I'd suggest that driver initialization should fail instead -- there's no reason to keep the cpufreq infrastructure up and running if nothing at all can be done, e.g. the frequency is fixed. The attached patch (untested due to lack of hardware) should do right that. Dave, please decide which patch you prefer, and merge accordingly.

Thanks,
Dominik

arch/i386/kernel/cpu/cpufreq/longrun.c +3 -0
diff -ruN linux-original/arch/i386/kernel/cpu/cpufreq/longrun.c linux/arch/i386/kernel/cpu/cpufreq/longrun.c
@@ -239,6 +239,9 @@
 	if (result)
 		return result;
 
+	if (longrun_high_freq <= longrun_low_freq)
+		return -ENODEV; /* degenerate Longrun table */
+
 	/* cpuinfo and default policy values */
 	policy->cpuinfo.min_freq = longrun_low_freq;
 	policy->cpuinfo.max_freq = longrun_high_freq;