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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 /init/calibrate.c
parent33b1e6939f5c37ab8e64280fd3d54046607b5c80 (diff)
downloadvexpress-lsk-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>
Diffstat (limited to 'init/calibrate.c')
-rw-r--r--init/calibrate.c14
1 files changed, 8 insertions, 6 deletions
diff --git a/init/calibrate.c b/init/calibrate.c
index 2568d22a304..aae2f40fea4 100644
--- a/init/calibrate.c
+++ b/init/calibrate.c
@@ -245,30 +245,32 @@ recalibrate:
void __cpuinit calibrate_delay(void)
{
+ unsigned long lpj;
static bool printed;
if (preset_lpj) {
- loops_per_jiffy = preset_lpj;
+ lpj = preset_lpj;
if (!printed)
pr_info("Calibrating delay loop (skipped) "
"preset value.. ");
} else if ((!printed) && lpj_fine) {
- loops_per_jiffy = lpj_fine;
+ lpj = lpj_fine;
pr_info("Calibrating delay loop (skipped), "
"value calculated using timer frequency.. ");
- } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
+ } else if ((lpj = calibrate_delay_direct()) != 0) {
if (!printed)
pr_info("Calibrating delay using timer "
"specific routine.. ");
} else {
if (!printed)
pr_info("Calibrating delay loop... ");
- loops_per_jiffy = calibrate_delay_converge();
+ lpj = calibrate_delay_converge();
}
if (!printed)
pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
- loops_per_jiffy/(500000/HZ),
- (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
+ lpj/(500000/HZ),
+ (lpj/(5000/HZ)) % 100, lpj);
+ loops_per_jiffy = lpj;
printed = true;
}