From 33182d15c6bf182f7ae32a66ea4a547d979cd6d7 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 8 Aug 2017 16:56:36 +1000 Subject: md: always clear ->safemode when md_check_recovery gets the mddev lock. If ->safemode == 1, md_check_recovery() will try to get the mddev lock and perform various other checks. If mddev->in_sync is zero, it will call set_in_sync, and clear ->safemode. However if mddev->in_sync is not zero, ->safemode will not be cleared. When md_check_recovery() drops the mddev lock, the thread is woken up again. Normally it would just check if there was anything else to do, find nothing, and go to sleep. However as ->safemode was not cleared, it will take the mddev lock again, then wake itself up when unlocking. This results in an infinite loop, repeatedly calling md_check_recovery(), which RCU or the soft-lockup detector will eventually complain about. Prior to commit 4ad23a976413 ("MD: use per-cpu counter for writes_pending"), safemode would only be set to one when the writes_pending counter reached zero, and would be cleared again when writes_pending is incremented. Since that patch, safemode is set more freely, but is not reliably cleared. So in md_check_recovery() clear ->safemode before checking ->in_sync. Fixes: 4ad23a976413 ("MD: use per-cpu counter for writes_pending") Cc: stable@vger.kernel.org (4.12+) Reported-by: Dominik Brodowski Reported-by: David R Signed-off-by: NeilBrown Signed-off-by: Shaohua Li --- drivers/md/md.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'drivers/md/md.c') diff --git a/drivers/md/md.c b/drivers/md/md.c index c99634612fc4..d84aceede1cb 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -8656,6 +8656,9 @@ void md_check_recovery(struct mddev *mddev) if (mddev_trylock(mddev)) { int spares = 0; + if (mddev->safemode == 1) + mddev->safemode = 0; + if (mddev->ro) { struct md_rdev *rdev; if (!mddev->external && mddev->in_sync) -- cgit v1.2.3 From 81fe48e9aa00bdd509bd3c37a76d1132da6b9f09 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 8 Aug 2017 16:56:36 +1000 Subject: md: fix test in md_write_start() md_write_start() needs to clear the in_sync flag is it is set, or if there might be a race with set_in_sync() such that the later will set it very soon. In the later case it is sufficient to take the spinlock to synchronize with set_in_sync(), and then set the flag if needed. The current test is incorrect. It should be: if "flag is set" or "race is possible" "flag is set" is trivially "mddev->in_sync". "race is possible" should be tested by "mddev->sync_checkers". If sync_checkers is 0, then there can be no race. set_in_sync() will wait in percpu_ref_switch_to_atomic_sync() for an RCU grace period, and as md_write_start() holds the rcu_read_lock(), set_in_sync() will be sure ot see the update to writes_pending. If sync_checkers is > 0, there could be race. If md_write_start() happened entirely between if (!mddev->in_sync && percpu_ref_is_zero(&mddev->writes_pending)) { and mddev->in_sync = 1; in set_in_sync(), then it would not see that is_sync had been set, and set_in_sync() would not see that writes_pending had been incremented. This bug means that in_sync is sometimes not set when it should be. Consequently there is a small chance that the array will be marked as "clean" when in fact it is inconsistent. Fixes: 4ad23a976413 ("MD: use per-cpu counter for writes_pending") cc: stable@vger.kernel.org (v4.12+) Signed-off-by: NeilBrown Signed-off-by: Shaohua Li --- drivers/md/md.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/md/md.c') diff --git a/drivers/md/md.c b/drivers/md/md.c index d84aceede1cb..e4ba95f6cd59 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -7996,7 +7996,7 @@ bool md_write_start(struct mddev *mddev, struct bio *bi) if (mddev->safemode == 1) mddev->safemode = 0; /* sync_checkers is always 0 when writes_pending is in per-cpu mode */ - if (mddev->in_sync || !mddev->sync_checkers) { + if (mddev->in_sync || mddev->sync_checkers) { spin_lock(&mddev->lock); if (mddev->in_sync) { mddev->in_sync = 0; -- cgit v1.2.3 From afc1f55ca44e257f69da8f43e0714a76686ae8d1 Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Fri, 11 Aug 2017 20:34:45 -0700 Subject: MD: not clear ->safemode for external metadata array ->safemode should be triggered by mdadm for external metadaa array, otherwise array's state confuses mdadm. Fixes: 33182d15c6bf(md: always clear ->safemode when md_check_recovery gets the mddev lock.) Cc: NeilBrown Signed-off-by: Shaohua Li --- drivers/md/md.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/md/md.c') diff --git a/drivers/md/md.c b/drivers/md/md.c index e4ba95f6cd59..b01e458d31e9 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -8656,7 +8656,7 @@ void md_check_recovery(struct mddev *mddev) if (mddev_trylock(mddev)) { int spares = 0; - if (mddev->safemode == 1) + if (!mddev->external && mddev->safemode == 1) mddev->safemode = 0; if (mddev->ro) { -- cgit v1.2.3