Eric Lee / smarc-ti-linux-kernel

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Commit 6ffc787a4492ac627315aaeafdfdc0a5c3028582

Authored by David Fries
Committed by Linus Torvalds
1 parent 82f560874e
Exists in master and in 20 other branches dlt-processor-sdk-linux-03.00.00.04, newt-ti-linux-3.12.y, processor-sdk-linux-01.00.00, processor-sdk-linux-02.00.01, smarc-ti-linux-3.12.10, smarc-ti-linux-3.12.y, smarc-ti-linux-3.14.y, smarc-ti-linux-3.15.y, smarc-ti-lsk-linux-4.1.y, smarct3x-processor-sdk-04.01.00.06, smarct3x-processor-sdk-linux-02.00.01, smarct3x-processor-sdk-linux-03.00.00.04, smarct4x-800-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-04.01.00.06, smarct4x-processor-sdk-linux-02.00.01, smarct4x-processor-sdk-linux-03.00.00.04, ti-linux-3.12.y, ti-linux-3.14.y, ti-linux-3.15.y, ti-lsk-linux-4.1.y

system timer: fix crash in <100Hz system timer 

The kernel has a divide by zero crash when trying to run the system timer
less than 100Hz.  The problem is x/(HZ/USER_HZ) and related.  Now
x*(USER_HZ/HZ) will be used if HZ<USER_HZ.

I'm running the Linux kernel under qemu and went to run a slower system
timer to take less CPU (and battery) on the host.  I found that the kernel
paniced under emulation because of a divide by zero in three places.  Here
is the patch.  The base git was updated today 01-05-2008.  I went for a
20Hz system time by adding config HZ_20 etc to kernel/Kconfig.hz.  With
this patch I verified the system timer by looking at /proc/interrupts.

[akpm@linux-foundation.org: partially clean up the macro maze]
Signed-off-by: David Fries <david@fries.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 2 changed files with 13 additions and 2 deletions Side-by-side Diff

include/linux/acct.h
Diff comments   View file @ 6ffc787
... ... @@ -173,7 +173,11 @@
173 173 static inline u32 jiffies_to_AHZ(unsigned long x)
174 174 {
175 175 #if (TICK_NSEC % (NSEC_PER_SEC / AHZ)) == 0
  176 +# if HZ < AHZ
  177 + return x * (AHZ / HZ);
  178 +# else
176 179 return x / (HZ / AHZ);
  180 +# endif
177 181 #else
178 182 u64 tmp = (u64)x * TICK_NSEC;
179 183 do_div(tmp, (NSEC_PER_SEC / AHZ));
... ... @@ -566,7 +566,11 @@
566 566 clock_t jiffies_to_clock_t(long x)
567 567 {
568 568 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
  569 +# if HZ < USER_HZ
  570 + return x * (USER_HZ / HZ);
  571 +# else
569 572 return x / (HZ / USER_HZ);
  573 +# endif
570 574 #else
571 575 u64 tmp = (u64)x * TICK_NSEC;
572 576 do_div(tmp, (NSEC_PER_SEC / USER_HZ));
573 577  
... ... @@ -599,7 +603,12 @@
599 603 u64 jiffies_64_to_clock_t(u64 x)
600 604 {
601 605 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
  606 +# if HZ < USER_HZ
  607 + x *= USER_HZ;
  608 + do_div(x, HZ);
  609 +# else
602 610 do_div(x, HZ / USER_HZ);
  611 +# endif
603 612 #else
604 613 /*
605 614 * There are better ways that don't overflow early,
... ... @@ -611,7 +620,6 @@
611 620 #endif
612 621 return x;
613 622 }
614   -
615 623 EXPORT_SYMBOL(jiffies_64_to_clock_t);
616 624  
617 625 u64 nsec_to_clock_t(u64 x)
... ... @@ -646,7 +654,6 @@
646 654 } while (read_seqretry(&xtime_lock, seq));
647 655 return ret;
648 656 }
649   -
650 657 EXPORT_SYMBOL(get_jiffies_64);
651 658 #endif
652 659