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Russell King 1b19ca9f0b Fix CPU spinlock lockups on secondary CPU bringup 
Secondary CPU bringup typically calls calibrate_delay() during its
initialization.  However, calibrate_delay() modifies a global variable
(loops_per_jiffy) used for udelay() and __delay().

A side effect of 71c696b1 ("calibrate: extract fall-back calculation
into own helper") introduced in the 2.6.39 merge window means that we
end up with a substantial period where loops_per_jiffy is zero.  This
causes the spinlock debugging code to malfunction:

	u64 loops = loops_per_jiffy * HZ;
	for (;;) {
		for (i = 0; i < loops; i++) {
			if (arch_spin_trylock(&lock->raw_lock))
				return;
			__delay(1);
		}
		...
	}

by never calling arch_spin_trylock() - resulting in the CPU locking
up in an infinite loop inside __spin_lock_debug().

Work around this by only writing to loops_per_jiffy only once we have
completed all the calibration decisions.

Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: <stable@kernel.org> (2.6.39-stable)
--
Better solutions (such as omitting the calibration for secondary CPUs,
or arranging for calibrate_delay() to return the LPJ value and leave
it to the caller to decide where to store it) are a possibility, but
would be much more invasive into each architecture.

I think this is the best solution for -rc and stable, but it should be
revisited for the next merge window.

 init/calibrate.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2011-06-23 08:59:38 -07:00
..
Kconfig gcov: disable CONFIG_CONSTRUCTORS when not needed by CONFIG_GCOV_KERNEL 2011-06-15 20:04:01 -07:00
Makefile kbuild: move compile.h to include/generated 2009-12-12 13:08:14 +01:00
calibrate.c Fix CPU spinlock lockups on secondary CPU bringup 2011-06-23 08:59:38 -07:00
do_mounts.c Fix common misspellings 2011-03-31 11:26:23 -03:00
do_mounts.h md: move lots of #include lines out of .h files and into .c 2009-03-31 14:33:13 +11:00
do_mounts_initrd.c Make do_execve() take a const filename pointer 2010-08-17 18:07:43 -07:00
do_mounts_md.c init: mark __user address space on string literals 2010-10-26 16:52:15 -07:00
do_mounts_rd.c init: return proper error code in do_mounts_rd() 2011-03-22 17:44:15 -07:00
initramfs.c Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild-2.6 2010-10-28 15:13:55 -07:00
main.c generic-ipi: Fix kexec boot crash by initializing call_single_queue before enabling interrupts 2011-06-17 10:17:12 +02:00
noinitramfs.c init: mark __user address space on string literals 2010-10-26 16:52:15 -07:00
version.c userns: add a user_namespace as creator/owner of uts_namespace 2011-03-23 19:46:59 -07:00