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authorRussell King <rmk+kernel@arm.linux.org.uk>2011-06-22 11:55:50 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2011-06-23 08:59:38 -0700
commit1b19ca9f0bdab7d5035821e1ec8f39df9a6e3ee0 (patch)
tree3c2d550bba679b7c88c01c066cac696f2d19ffbb /fs/omfs
parent33b1e6939f5c37ab8e64280fd3d54046607b5c80 (diff)
downloadlinux-linaro-stable-1b19ca9f0bdab7d5035821e1ec8f39df9a6e3ee0.tar.gz
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>
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