From 4812c54dc0498c4b757cbc7f41c1999b5a1c9f67 Mon Sep 17 00:00:00 2001 From: John Stultz Date: Fri, 22 Sep 2023 04:35:59 +0000 Subject: locking/ww_mutex/test: Use prng instead of rng to avoid hangs at bootup Booting w/ qemu without kvm, and with 64 cpus, I noticed we'd sometimes hung task watchdog splats in get_random_u32_below() when using the test-ww_mutex stress test. While entropy exhaustion is no longer an issue, the RNG may be slower early in boot. The test-ww_mutex code will spawn off 128 threads (2x cpus) and each thread will call get_random_u32_below() a number of times to generate a random order of the 16 locks. This intense use takes time and without kvm, qemu can be slow enough that we trip the hung task watchdogs. For this test, we don't need true randomness, just mixed up orders for testing ww_mutex lock acquisitions, so it changes the logic to use the prng instead, which takes less time and avoids the watchdgos. Feedback would be appreciated! Signed-off-by: John Stultz Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230922043616.19282-2-jstultz@google.com --- kernel/locking/test-ww_mutex.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'kernel/locking') diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c index 93cca6e69860..9bceba65858a 100644 --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -9,7 +9,7 @@ #include #include #include -#include +#include #include #include @@ -386,6 +386,19 @@ struct stress { int nlocks; }; +struct rnd_state rng; +DEFINE_SPINLOCK(rng_lock); + +static inline u32 prandom_u32_below(u32 ceil) +{ + u32 ret; + + spin_lock(&rng_lock); + ret = prandom_u32_state(&rng) % ceil; + spin_unlock(&rng_lock); + return ret; +} + static int *get_random_order(int count) { int *order; @@ -399,7 +412,7 @@ static int *get_random_order(int count) order[n] = n; for (n = count - 1; n > 1; n--) { - r = get_random_u32_below(n + 1); + r = prandom_u32_below(n + 1); if (r != n) { tmp = order[n]; order[n] = order[r]; @@ -625,6 +638,8 @@ static int __init test_ww_mutex_init(void) printk(KERN_INFO "Beginning ww mutex selftests\n"); + prandom_seed_state(&rng, get_random_u64()); + wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0); if (!wq) return -ENOMEM; -- cgit v1.2.3