[PATCH v7 1/8] dax: Use rwsem for dax_{read,write}_lock()

[Shiyang Ruan <ruansy.fnst@fujitsu.com>]

In order to introduce dax holder registration, we need a write lock for
dax.  Because of the rarity of notification failures and the infrequency
of registration events, it would be better to be a global lock rather
than per-device.  So, change the current lock to rwsem and introduce a
write lock for registration.

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
 drivers/dax/device.c       | 11 +++++-----
 drivers/dax/super.c        | 43 ++++++++++++++++++++++----------------
 drivers/md/dm-writecache.c |  7 +++----
 fs/dax.c                   | 26 +++++++++++------------
 include/linux/dax.h        |  9 ++++----
 5 files changed, 49 insertions(+), 47 deletions(-)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index dd8222a42808..cc7b835509f9 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -198,7 +198,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
 	struct file *filp = vmf->vma->vm_file;
 	unsigned long fault_size;
 	vm_fault_t rc = VM_FAULT_SIGBUS;
-	int id;
 	pfn_t pfn;
 	struct dev_dax *dev_dax = filp->private_data;
 
@@ -206,7 +205,7 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
 			(vmf->flags & FAULT_FLAG_WRITE) ? "write" : "read",
 			vmf->vma->vm_start, vmf->vma->vm_end, pe_size);
 
-	id = dax_read_lock();
+	dax_read_lock();
 	switch (pe_size) {
 	case PE_SIZE_PTE:
 		fault_size = PAGE_SIZE;
@@ -246,7 +245,7 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
 			page->index = pgoff + i;
 		}
 	}
-	dax_read_unlock(id);
+	dax_read_unlock();
 
 	return rc;
 }
@@ -284,7 +283,7 @@ static const struct vm_operations_struct dax_vm_ops = {
 static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
 {
 	struct dev_dax *dev_dax = filp->private_data;
-	int rc, id;
+	int rc;
 
 	dev_dbg(&dev_dax->dev, "trace\n");
 
@@ -292,9 +291,9 @@ static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
 	 * We lock to check dax_dev liveness and will re-check at
 	 * fault time.
 	 */
-	id = dax_read_lock();
+	dax_read_lock();
 	rc = check_vma(dev_dax, vma, __func__);
-	dax_read_unlock(id);
+	dax_read_unlock();
 	if (rc)
 		return rc;
 
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index fc89e91beea7..48ce86501d93 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -36,7 +36,7 @@ struct dax_device {
 };
 
 static dev_t dax_devt;
-DEFINE_STATIC_SRCU(dax_srcu);
+static DECLARE_RWSEM(dax_rwsem);
 static struct vfsmount *dax_mnt;
 static DEFINE_IDA(dax_minor_ida);
 static struct kmem_cache *dax_cache __read_mostly;
@@ -46,18 +46,28 @@ static struct super_block *dax_superblock __read_mostly;
 static struct hlist_head dax_host_list[DAX_HASH_SIZE];
 static DEFINE_SPINLOCK(dax_host_lock);
 
-int dax_read_lock(void)
+void dax_read_lock(void)
 {
-	return srcu_read_lock(&dax_srcu);
+	down_read(&dax_rwsem);
 }
 EXPORT_SYMBOL_GPL(dax_read_lock);
 
-void dax_read_unlock(int id)
+void dax_read_unlock(void)
 {
-	srcu_read_unlock(&dax_srcu, id);
+	up_read(&dax_rwsem);
 }
 EXPORT_SYMBOL_GPL(dax_read_unlock);
 
+void dax_write_lock(void)
+{
+	down_write(&dax_rwsem);
+}
+
+void dax_write_unlock(void)
+{
+	up_write(&dax_rwsem);
+}
+
 static int dax_host_hash(const char *host)
 {
 	return hashlen_hash(hashlen_string("DAX", host)) % DAX_HASH_SIZE;
@@ -70,14 +80,14 @@ static int dax_host_hash(const char *host)
 static struct dax_device *dax_get_by_host(const char *host)
 {
 	struct dax_device *dax_dev, *found = NULL;
-	int hash, id;
+	int hash;
 
 	if (!host)
 		return NULL;
 
 	hash = dax_host_hash(host);
 
-	id = dax_read_lock();
+	dax_read_lock();
 	spin_lock(&dax_host_lock);
 	hlist_for_each_entry(dax_dev, &dax_host_list[hash], list) {
 		if (!dax_alive(dax_dev)
@@ -89,7 +99,7 @@ static struct dax_device *dax_get_by_host(const char *host)
 		break;
 	}
 	spin_unlock(&dax_host_lock);
-	dax_read_unlock(id);
+	dax_read_unlock();
 
 	return found;
 }
@@ -130,7 +140,7 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
 	pfn_t pfn, end_pfn;
 	sector_t last_page;
 	long len, len2;
-	int err, id;
+	int err;
 
 	if (blocksize != PAGE_SIZE) {
 		pr_info("%pg: error: unsupported blocksize for dax\n", bdev);
@@ -155,14 +165,14 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
 		return false;
 	}
 
-	id = dax_read_lock();
+	dax_read_lock();
 	len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
 	len2 = dax_direct_access(dax_dev, pgoff_end, 1, &end_kaddr, &end_pfn);
 
 	if (len < 1 || len2 < 1) {
 		pr_info("%pg: error: dax access failed (%ld)\n",
 				bdev, len < 1 ? len : len2);
-		dax_read_unlock(id);
+		dax_read_unlock();
 		return false;
 	}
 
@@ -192,7 +202,7 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
 		put_dev_pagemap(end_pgmap);
 
 	}
-	dax_read_unlock(id);
+	dax_read_unlock();
 
 	if (!dax_enabled) {
 		pr_info("%pg: error: dax support not enabled\n", bdev);
@@ -206,16 +216,15 @@ bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
 		int blocksize, sector_t start, sector_t len)
 {
 	bool ret = false;
-	int id;
 
 	if (!dax_dev)
 		return false;
 
-	id = dax_read_lock();
+	dax_read_lock();
 	if (dax_alive(dax_dev) && dax_dev->ops->dax_supported)
 		ret = dax_dev->ops->dax_supported(dax_dev, bdev, blocksize,
 						  start, len);
-	dax_read_unlock(id);
+	dax_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(dax_supported);
@@ -410,7 +419,7 @@ EXPORT_SYMBOL_GPL(__set_dax_synchronous);
 
 bool dax_alive(struct dax_device *dax_dev)
 {
-	lockdep_assert_held(&dax_srcu);
+	lockdep_assert_held(&dax_rwsem);
 	return test_bit(DAXDEV_ALIVE, &dax_dev->flags);
 }
 EXPORT_SYMBOL_GPL(dax_alive);
@@ -428,8 +437,6 @@ void kill_dax(struct dax_device *dax_dev)
 
 	clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
 
-	synchronize_srcu(&dax_srcu);
-
 	spin_lock(&dax_host_lock);
 	hlist_del_init(&dax_dev->list);
 	spin_unlock(&dax_host_lock);
diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 18320444fb0a..1067b3e98220 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -260,7 +260,6 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 	loff_t s;
 	long p, da;
 	pfn_t pfn;
-	int id;
 	struct page **pages;
 	sector_t offset;
 
@@ -284,7 +283,7 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 	}
 	offset >>= PAGE_SHIFT - 9;
 
-	id = dax_read_lock();
+	dax_read_lock();
 
 	da = dax_direct_access(wc->ssd_dev->dax_dev, offset, p, &wc->memory_map, &pfn);
 	if (da < 0) {
@@ -334,7 +333,7 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 		wc->memory_vmapped = true;
 	}
 
-	dax_read_unlock(id);
+	dax_read_unlock();
 
 	wc->memory_map += (size_t)wc->start_sector << SECTOR_SHIFT;
 	wc->memory_map_size -= (size_t)wc->start_sector << SECTOR_SHIFT;
@@ -343,7 +342,7 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 err3:
 	kvfree(pages);
 err2:
-	dax_read_unlock(id);
+	dax_read_unlock();
 err1:
 	return r;
 }
diff --git a/fs/dax.c b/fs/dax.c
index 4e3e5a283a91..798c43f09eee 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -715,22 +715,21 @@ static int copy_cow_page_dax(struct block_device *bdev, struct dax_device *dax_d
 	void *vto, *kaddr;
 	pgoff_t pgoff;
 	long rc;
-	int id;
 
 	rc = bdev_dax_pgoff(bdev, sector, PAGE_SIZE, &pgoff);
 	if (rc)
 		return rc;
 
-	id = dax_read_lock();
+	dax_read_lock();
 	rc = dax_direct_access(dax_dev, pgoff, 1, &kaddr, NULL);
 	if (rc < 0) {
-		dax_read_unlock(id);
+		dax_read_unlock();
 		return rc;
 	}
 	vto = kmap_atomic(to);
 	copy_user_page(vto, (void __force *)kaddr, vaddr, to);
 	kunmap_atomic(vto);
-	dax_read_unlock(id);
+	dax_read_unlock();
 	return 0;
 }
 
@@ -1015,13 +1014,13 @@ static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
 {
 	const sector_t sector = dax_iomap_sector(iomap, pos);
 	pgoff_t pgoff;
-	int id, rc;
+	int rc;
 	long length;
 
 	rc = bdev_dax_pgoff(iomap->bdev, sector, size, &pgoff);
 	if (rc)
 		return rc;
-	id = dax_read_lock();
+	dax_read_lock();
 	length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
 				   NULL, pfnp);
 	if (length < 0) {
@@ -1038,7 +1037,7 @@ static int dax_iomap_pfn(const struct iomap *iomap, loff_t pos, size_t size,
 		goto out;
 	rc = 0;
 out:
-	dax_read_unlock(id);
+	dax_read_unlock();
 	return rc;
 }
 
@@ -1130,7 +1129,7 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 {
 	sector_t sector = iomap_sector(iomap, pos & PAGE_MASK);
 	pgoff_t pgoff;
-	long rc, id;
+	long rc;
 	void *kaddr;
 	bool page_aligned = false;
 	unsigned offset = offset_in_page(pos);
@@ -1144,14 +1143,14 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 	if (rc)
 		return rc;
 
-	id = dax_read_lock();
+	dax_read_lock();
 
 	if (page_aligned)
 		rc = dax_zero_page_range(iomap->dax_dev, pgoff, 1);
 	else
 		rc = dax_direct_access(iomap->dax_dev, pgoff, 1, &kaddr, NULL);
 	if (rc < 0) {
-		dax_read_unlock(id);
+		dax_read_unlock();
 		return rc;
 	}
 
@@ -1159,7 +1158,7 @@ s64 dax_iomap_zero(loff_t pos, u64 length, struct iomap *iomap)
 		memset(kaddr + offset, 0, size);
 		dax_flush(iomap->dax_dev, kaddr + offset, size);
 	}
-	dax_read_unlock(id);
+	dax_read_unlock();
 	return size;
 }
 
@@ -1174,7 +1173,6 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 	loff_t end = pos + length, done = 0;
 	ssize_t ret = 0;
 	size_t xfer;
-	int id;
 
 	if (iov_iter_rw(iter) == READ) {
 		end = min(end, i_size_read(iomi->inode));
@@ -1199,7 +1197,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 					      (end - 1) >> PAGE_SHIFT);
 	}
 
-	id = dax_read_lock();
+	dax_read_lock();
 	while (pos < end) {
 		unsigned offset = pos & (PAGE_SIZE - 1);
 		const size_t size = ALIGN(length + offset, PAGE_SIZE);
@@ -1251,7 +1249,7 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
 		if (xfer < map_len)
 			break;
 	}
-	dax_read_unlock(id);
+	dax_read_unlock();
 
 	return done ? done : ret;
 }
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 2619d94c308d..097b3304f9b9 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -177,15 +177,14 @@ static inline void dax_unlock_page(struct page *page, dax_entry_t cookie)
 #endif
 
 #if IS_ENABLED(CONFIG_DAX)
-int dax_read_lock(void);
-void dax_read_unlock(int id);
+void dax_read_lock(void);
+void dax_read_unlock(void);
 #else
-static inline int dax_read_lock(void)
+static inline void dax_read_lock(void)
 {
-	return 0;
 }
 
-static inline void dax_read_unlock(int id)
+static inline void dax_read_unlock(void)
 {
 }
 #endif /* CONFIG_DAX */
-- 
2.33.0