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


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