system timer: fix crash in <100Hz system timer (6ffc787a) · Commits · 戴 / test

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>

include/linux/acct.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -173,7 +173,11 @@ typedef struct acct acct_t;
		static inline u32 jiffies_to_AHZ(unsigned long x)
		{
		#if (TICK_NSEC % (NSEC_PER_SEC / AHZ)) == 0
		# if HZ < AHZ
		return x * (AHZ / HZ);
		# else
		return x / (HZ / AHZ);
		# endif
		#else
		u64 tmp = (u64)x * TICK_NSEC;
		do_div(tmp, (NSEC_PER_SEC / AHZ));

kernel/time.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -566,7 +566,11 @@ EXPORT_SYMBOL(jiffies_to_timeval);
		clock_t jiffies_to_clock_t(long x)
		{
		#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
		# if HZ < USER_HZ
		return x * (USER_HZ / HZ);
		# else
		return x / (HZ / USER_HZ);
		# endif
		#else
		u64 tmp = (u64)x * TICK_NSEC;
		do_div(tmp, (NSEC_PER_SEC / USER_HZ));
		@@ -599,7 +603,12 @@ EXPORT_SYMBOL(clock_t_to_jiffies);
		u64 jiffies_64_to_clock_t(u64 x)
		{
		#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
		# if HZ < USER_HZ
		x *= USER_HZ;
		do_div(x, HZ);
		# else
		do_div(x, HZ / USER_HZ);
		# endif
		#else
		/*
		* There are better ways that don't overflow early,
		@@ -611,7 +620,6 @@ u64 jiffies_64_to_clock_t(u64 x)
		#endif
		return x;
		}

		EXPORT_SYMBOL(jiffies_64_to_clock_t);

		u64 nsec_to_clock_t(u64 x)
		@@ -646,7 +654,6 @@ u64 get_jiffies_64(void)
		} while (read_seqretry(&xtime_lock, seq));
		return ret;
		}

		EXPORT_SYMBOL(get_jiffies_64);
		#endif

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