libnvdimm: fix clear poison locking with spinlock and GFP_NOWAIT allocation

The following warning results from holding a lane spinlock,
preempt_disable(), or the btt map spinlock and then trying to take the
reconfig_mutex to walk the poison list and potentially add new entries.

BUG: sleeping function called from invalid context at kernel/locking/mutex.
c:747
in_atomic(): 1, irqs_disabled(): 0, pid: 17159, name: dd
[..]
Call Trace:
dump_stack+0x85/0xc8
___might_sleep+0x184/0x250
__might_sleep+0x4a/0x90
__mutex_lock+0x58/0x9b0
? nvdimm_bus_lock+0x21/0x30 [libnvdimm]
? __nvdimm_bus_badblocks_clear+0x2f/0x60 [libnvdimm]
? acpi_nfit_forget_poison+0x79/0x80 [nfit]
? _raw_spin_unlock+0x27/0x40
mutex_lock_nested+0x1b/0x20
nvdimm_bus_lock+0x21/0x30 [libnvdimm]
nvdimm_forget_poison+0x25/0x50 [libnvdimm]
nvdimm_clear_poison+0x106/0x140 [libnvdimm]
nsio_rw_bytes+0x164/0x270 [libnvdimm]
btt_write_pg+0x1de/0x3e0 [nd_btt]
? blk_queue_enter+0x30/0x290
btt_make_request+0x11a/0x310 [nd_btt]
? blk_queue_enter+0xb7/0x290
? blk_queue_enter+0x30/0x290
generic_make_request+0x118/0x3b0

A spinlock is introduced to protect the poison list. This allows us to not
having to acquire the reconfig_mutex for touching the poison list. The
add_poison() function has been broken out into two helper functions. One to
allocate the poison entry and the other to apppend the entry. This allows us
to unlock the poison_lock in non-I/O path and continue to be able to allocate
the poison entry with GFP_KERNEL. We will use GFP_NOWAIT in the I/O path in
order to satisfy being in atomic context.

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/nvdimm/core.c

@@ -518,6 +518,15 @@ void nvdimm_badblocks_populate(struct nd_region *nd_region,
 }
 EXPORT_SYMBOL_GPL(nvdimm_badblocks_populate);
 
+static void append_poison_entry(struct nvdimm_bus *nvdimm_bus,
+		struct nd_poison *pl, u64 addr, u64 length)
+{
+	lockdep_assert_held(&nvdimm_bus->poison_lock);
+	pl->start = addr;
+	pl->length = length;
+	list_add_tail(&pl->list, &nvdimm_bus->poison_list);
+}
+
 static int add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length,
 			gfp_t flags)
 {
@@ -527,19 +536,24 @@ static int add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length,
 	if (!pl)
 		return -ENOMEM;
 
-	pl->start = addr;
-	pl->length = length;
-	list_add_tail(&pl->list, &nvdimm_bus->poison_list);
-
+	append_poison_entry(nvdimm_bus, pl, addr, length);
 	return 0;
 }
 
 static int bus_add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length)
 {
-	struct nd_poison *pl;
+	struct nd_poison *pl, *pl_new;
 
-	if (list_empty(&nvdimm_bus->poison_list))
-		return add_poison(nvdimm_bus, addr, length, GFP_KERNEL);
+	spin_unlock(&nvdimm_bus->poison_lock);
+	pl_new = kzalloc(sizeof(*pl_new), GFP_KERNEL);
+	spin_lock(&nvdimm_bus->poison_lock);
+
+	if (list_empty(&nvdimm_bus->poison_list)) {
+		if (!pl_new)
+			return -ENOMEM;
+		append_poison_entry(nvdimm_bus, pl_new, addr, length);
+		return 0;
+	}
 
 	/*
 	 * There is a chance this is a duplicate, check for those first.
@@ -551,6 +565,7 @@ static int bus_add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length)
 			/* If length has changed, update this list entry */
 			if (pl->length != length)
 				pl->length = length;
+			kfree(pl_new);
 			return 0;
 		}
 
@@ -559,30 +574,33 @@ static int bus_add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length)
 	 * as any overlapping ranges will get resolved when the list is consumed
 	 * and converted to badblocks
 	 */
-	return add_poison(nvdimm_bus, addr, length, GFP_KERNEL);
+	if (!pl_new)
+		return -ENOMEM;
+	append_poison_entry(nvdimm_bus, pl_new, addr, length);
+
+	return 0;
 }
 
 int nvdimm_bus_add_poison(struct nvdimm_bus *nvdimm_bus, u64 addr, u64 length)
 {
 	int rc;
 
-	nvdimm_bus_lock(&nvdimm_bus->dev);
+	spin_lock(&nvdimm_bus->poison_lock);
 	rc = bus_add_poison(nvdimm_bus, addr, length);
-	nvdimm_bus_unlock(&nvdimm_bus->dev);
+	spin_unlock(&nvdimm_bus->poison_lock);
 
 	return rc;
 }
 EXPORT_SYMBOL_GPL(nvdimm_bus_add_poison);
 
-void __nvdimm_forget_poison(struct nvdimm_bus *nvdimm_bus, phys_addr_t start,
+void nvdimm_forget_poison(struct nvdimm_bus *nvdimm_bus, phys_addr_t start,
 		unsigned int len)
 {
 	struct list_head *poison_list = &nvdimm_bus->poison_list;
 	u64 clr_end = start + len - 1;
 	struct nd_poison *pl, *next;
 
-	lockdep_assert_held(&nvdimm_bus->reconfig_mutex);
-
+	spin_lock(&nvdimm_bus->poison_lock);
 	WARN_ON_ONCE(list_empty(poison_list));
 
 	/*
@@ -629,21 +647,13 @@ void __nvdimm_forget_poison(struct nvdimm_bus *nvdimm_bus, phys_addr_t start,
 			u64 new_len = pl_end - new_start + 1;
 
 			/* Add new entry covering the right half */
-			add_poison(nvdimm_bus, new_start, new_len, GFP_NOIO);
+			add_poison(nvdimm_bus, new_start, new_len, GFP_NOWAIT);
 			/* Adjust this entry to cover the left half */
 			pl->length = start - pl->start;
 			continue;
 		}
 	}
-}
-EXPORT_SYMBOL_GPL(__nvdimm_forget_poison);
-
-void nvdimm_forget_poison(struct nvdimm_bus *nvdimm_bus,
-		phys_addr_t start, unsigned int len)
-{
-	nvdimm_bus_lock(&nvdimm_bus->dev);
-	__nvdimm_forget_poison(nvdimm_bus, start, len);
-	nvdimm_bus_unlock(&nvdimm_bus->dev);
+	spin_unlock(&nvdimm_bus->poison_lock);
 }
 EXPORT_SYMBOL_GPL(nvdimm_forget_poison);