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author | Russell King <rmk+kernel@arm.linux.org.uk> | 2011-06-22 12:55:50 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-06-23 17:59:38 +0200 |
commit | 1b19ca9f0bdab7d5035821e1ec8f39df9a6e3ee0 (patch) | |
tree | 3c2d550bba679b7c88c01c066cac696f2d19ffbb | |
parent | serial: mrst_max3110: initialize waitqueue earlier (diff) | |
download | linux-1b19ca9f0bdab7d5035821e1ec8f39df9a6e3ee0.tar.xz linux-1b19ca9f0bdab7d5035821e1ec8f39df9a6e3ee0.zip |
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>
-rw-r--r-- | init/calibrate.c | 14 |
1 files changed, 8 insertions, 6 deletions
diff --git a/init/calibrate.c b/init/calibrate.c index 2568d22a304e..aae2f40fea4c 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; } |