From c17922b8a9db00ad7e7d59a5ff975b2a1edcf887 Mon Sep 17 00:00:00 2001 From: Olaf Faaland Date: Tue, 20 Feb 2018 17:33:51 -0800 Subject: [PATCH] Detect long config lock acquisition in mmp If something holds the config lock as a writer for too long, MMP will fail to issue MMP writes in a timely manner. This will result either in the pool being suspended, or in an extreme case, in the pool not being protected. If the time to acquire the config lock exceeds 1/10 of the minimum zfs_multihost_interval, report it in the zfs debug log. Reviewed-by: Brian Behlendorf Signed-off-by: Olaf Faaland Closes #7212 --- module/zfs/mmp.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/module/zfs/mmp.c b/module/zfs/mmp.c index ee8e9201b..634e48287 100644 --- a/module/zfs/mmp.c +++ b/module/zfs/mmp.c @@ -323,7 +323,13 @@ mmp_write_uberblock(spa_t *spa) int label; uint64_t offset; + hrtime_t lock_acquire_time = gethrtime(); spa_config_enter(spa, SCL_STATE, mmp_tag, RW_READER); + lock_acquire_time = gethrtime() - lock_acquire_time; + if (lock_acquire_time > (MSEC2NSEC(MMP_MIN_INTERVAL) / 10)) + zfs_dbgmsg("SCL_STATE acquisition took %llu ns\n", + (u_longlong_t)lock_acquire_time); + vd = mmp_random_leaf(spa->spa_root_vdev); if (vd == NULL) { spa_config_exit(spa, SCL_STATE, FTAG); -- 2.40.0