linux/arch
Thomas Gleixner a7f4255f90 x86: Derandom delay_tsc for 64 bit
Commit f0fbf0abc0 ("x86: integrate delay functions") converted
delay_tsc() into a random delay generator for 64 bit.  The reason is
that it merged the mostly identical versions of delay_32.c and
delay_64.c.  Though the subtle difference of the result was:

 static void delay_tsc(unsigned long loops)
 {
-	unsigned bclock, now;
+	unsigned long bclock, now;

Now the function uses rdtscl() which returns the lower 32bit of the
TSC. On 32bit that's not problematic as unsigned long is 32bit. On 64
bit this fails when the lower 32bit are close to wrap around when
bclock is read, because the following check

       if ((now - bclock) >= loops)
       	  	break;

evaluated to true on 64bit for e.g. bclock = 0xffffffff and now = 0
because the unsigned long (now - bclock) of these values results in
0xffffffff00000001 which is definitely larger than the loops
value. That explains Tvortkos observation:

"Because I am seeing udelay(500) (_occasionally_) being short, and
 that by delaying for some duration between 0us (yep) and 491us."

Make those variables explicitely u32 again, so this works for both 32
and 64 bit.

Reported-by: Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org # >= 2.6.27
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-03-09 12:43:27 -08:00
..
alpha alpha: fix 32/64-bit bug in futex support 2012-03-05 15:49:43 -08:00
arm IOMMU fixes for Linux v3.3-rc6 2012-03-09 07:26:25 -08:00
avr32 avr32: select generic atomic64_t support 2012-02-03 16:16:40 -08:00
blackfin Merge branch 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci 2012-01-11 18:50:26 -08:00
c6x C6X: fix KSTK_EIP and KSTK_ESP macros 2012-03-07 11:28:22 -05:00
cris lib: use generic pci_iomap on all architectures 2012-01-10 18:04:27 -08:00
frv Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
h8300 Merge branch 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci 2012-01-11 18:50:26 -08:00
hexagon lib: move GENERIC_IOMAP to lib/Kconfig 2011-11-24 22:21:19 +02:00
ia64 Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux 2012-01-18 15:51:48 -08:00
m32r Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
m68k m68k: Do not set global share for non-kernel shared pages 2012-02-07 11:25:57 +10:00
microblaze Revert "microblaze: Add topology init" 2012-01-31 09:06:52 +01:00
mips MIPS: traps.c: Fix typo 2012-02-20 18:33:20 +01:00
mn10300 Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
openrisc openrisc: Fix up audit_syscall_[entry|exit]() usage 2012-02-17 09:53:12 +01:00
parisc [PARISC] don't unconditionally override CROSS_COMPILE for 64 bit. 2012-02-28 09:39:28 -06:00
powerpc powerpc: Fix various issues with return to userspace 2012-02-22 16:48:53 +11:00
s390 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2012-03-01 18:22:55 -08:00
score score: fix off-by-one index into syscall table 2012-01-23 08:38:49 -08:00
sh SuperH fixes for 3.3-rc5 2012-02-24 08:56:51 -08:00
sparc lib: Fix multiple definitions of clz_tab 2012-02-02 10:34:23 +11:00
tile Merge branch 'for-next' of git://git.infradead.org/users/dhowells/linux-headers 2012-01-14 18:03:30 -08:00
um Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/audit 2012-01-17 16:41:31 -08:00
unicore32 Merge branch 'linux-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci 2012-01-11 18:50:26 -08:00
x86 x86: Derandom delay_tsc for 64 bit 2012-03-09 12:43:27 -08:00
xtensa xtensa: fix memscan() 2012-02-03 16:16:40 -08:00
.gitignore
Kconfig mm,x86,um: move CMPXCHG_DOUBLE config option 2012-01-12 20:13:03 -08:00