Merge tag 'v4.8' into patchwork

Linux 4.8

* tag 'v4.8': (1761 commits)
  Linux 4.8
  ARM: 8618/1: decompressor: reset ttbcr fields to use TTBR0 on ARMv7
  MIPS: CM: Fix mips_cm_max_vp_width for non-MT kernels on MT systems
  include/linux/property.h: fix typo/compile error
  ocfs2: fix deadlock on mmapped page in ocfs2_write_begin_nolock()
  mm: workingset: fix crash in shadow node shrinker caused by replace_page_cache_page()
  MAINTAINERS: Switch to kernel.org email address for Javi Merino
  x86/entry/64: Fix context tracking state warning when load_gs_index fails
  x86/boot: Initialize FPU and X86_FEATURE_ALWAYS even if we don't have CPUID
  x86/vdso: Fix building on big endian host
  x86/boot: Fix another __read_cr4() case on 486
  sctp: fix the issue sctp_diag uses lock_sock in rcu_read_lock
  sctp: change to check peer prsctp_capable when using prsctp polices
  sctp: remove prsctp_param from sctp_chunk
  sctp: move sent_count to the memory hole in sctp_chunk
  tg3: Avoid NULL pointer dereference in tg3_io_error_detected()
  x86/init: Fix cr4_init_shadow() on CR4-less machines
  MIPS: Fix detection of unsupported highmem with cache aliases
  MIPS: Malta: Fix IOCU disable switch read for MIPS64
  MIPS: Fix BUILD_ROLLBACK_PROLOGUE for microMIPS
  ...

1 files changed, 15 insertions, 31 deletions

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 51f76ddbe265..1b1ab4a1d132 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -96,7 +96,6 @@ struct r5l_log {
 	spinlock_t no_space_stripes_lock;
 
 	bool need_cache_flush;
-	bool in_teardown;
 };
 
 /*
@@ -704,31 +703,22 @@ static void r5l_write_super_and_discard_space(struct r5l_log *log,
 
 	mddev = log->rdev->mddev;
 	/*
-	 * This is to avoid a deadlock. r5l_quiesce holds reconfig_mutex and
-	 * wait for this thread to finish. This thread waits for
-	 * MD_CHANGE_PENDING clear, which is supposed to be done in
-	 * md_check_recovery(). md_check_recovery() tries to get
-	 * reconfig_mutex. Since r5l_quiesce already holds the mutex,
-	 * md_check_recovery() fails, so the PENDING never get cleared. The
-	 * in_teardown check workaround this issue.
+	 * Discard could zero data, so before discard we must make sure
+	 * superblock is updated to new log tail. Updating superblock (either
+	 * directly call md_update_sb() or depend on md thread) must hold
+	 * reconfig mutex. On the other hand, raid5_quiesce is called with
+	 * reconfig_mutex hold. The first step of raid5_quiesce() is waitting
+	 * for all IO finish, hence waitting for reclaim thread, while reclaim
+	 * thread is calling this function and waitting for reconfig mutex. So
+	 * there is a deadlock. We workaround this issue with a trylock.
+	 * FIXME: we could miss discard if we can't take reconfig mutex
 	 */
-	if (!log->in_teardown) {
-		set_mask_bits(&mddev->flags, 0,
-			      BIT(MD_CHANGE_DEVS) | BIT(MD_CHANGE_PENDING));
-		md_wakeup_thread(mddev->thread);
-		wait_event(mddev->sb_wait,
-			!test_bit(MD_CHANGE_PENDING, &mddev->flags) ||
-			log->in_teardown);
-		/*
-		 * r5l_quiesce could run after in_teardown check and hold
-		 * mutex first. Superblock might get updated twice.
-		 */
-		if (log->in_teardown)
-			md_update_sb(mddev, 1);
-	} else {
-		WARN_ON(!mddev_is_locked(mddev));
-		md_update_sb(mddev, 1);
-	}
+	set_mask_bits(&mddev->flags, 0,
+		BIT(MD_CHANGE_DEVS) | BIT(MD_CHANGE_PENDING));
+	if (!mddev_trylock(mddev))
+		return;
+	md_update_sb(mddev, 1);
+	mddev_unlock(mddev);
 
 	/* discard IO error really doesn't matter, ignore it */
 	if (log->last_checkpoint < end) {
@@ -827,7 +817,6 @@ void r5l_quiesce(struct r5l_log *log, int state)
 	if (!log || state == 2)
 		return;
 	if (state == 0) {
-		log->in_teardown = 0;
 		/*
 		 * This is a special case for hotadd. In suspend, the array has
 		 * no journal. In resume, journal is initialized as well as the
@@ -838,11 +827,6 @@ void r5l_quiesce(struct r5l_log *log, int state)
 		log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
 					log->rdev->mddev, "reclaim");
 	} else if (state == 1) {
-		/*
-		 * at this point all stripes are finished, so io_unit is at
-		 * least in STRIPE_END state
-		 */
-		log->in_teardown = 1;
 		/* make sure r5l_write_super_and_discard_space exits */
 		mddev = log->rdev->mddev;
 		wake_up(&mddev->sb_wait);