@@ -2327,6 +2327,7 @@ static ssize_t bch_pending_bdevs_cleanup(struct kobject *k,
kobj_attribute_write(register, register_bcache);
kobj_attribute_write(register_quiet, register_bcache);
+kobj_attribute_write(register_async, register_bcache);
kobj_attribute_write(pendings_cleanup, bch_pending_bdevs_cleanup);
static bool bch_is_open_backing(struct block_device *bdev)
@@ -2362,6 +2363,83 @@ static bool bch_is_open(struct block_device *bdev)
return bch_is_open_cache(bdev) || bch_is_open_backing(bdev);
}
+struct async_reg_args {
+ struct work_struct reg_work;
+ char *path;
+ struct cache_sb *sb;
+ struct cache_sb_disk *sb_disk;
+ struct block_device *bdev;
+};
+
+static void register_bdev_worker(struct work_struct *work)
+{
+ int fail = false;
+ struct async_reg_args *args =
+ container_of(work, struct async_reg_args, reg_work);
+ struct cached_dev *dc;
+
+ dc = kzalloc(sizeof(*dc), GFP_KERNEL);
+ if (!dc) {
+ fail = true;
+ put_page(virt_to_page(args->sb_disk));
+ blkdev_put(args->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+ goto out;
+ }
+
+ mutex_lock(&bch_register_lock);
+ if (register_bdev(args->sb, args->sb_disk, args->bdev, dc) < 0)
+ fail = true;
+ mutex_unlock(&bch_register_lock);
+
+out:
+ if (fail)
+ pr_info("error %s: fail to register backing device\n",
+ args->path);
+ kfree(args->sb);
+ kfree(args->path);
+ kfree(args);
+ module_put(THIS_MODULE);
+}
+
+static void register_cache_worker(struct work_struct *work)
+{
+ int fail = false;
+ struct async_reg_args *args =
+ container_of(work, struct async_reg_args, reg_work);
+ struct cache *ca;
+
+ ca = kzalloc(sizeof(*ca), GFP_KERNEL);
+ if (!ca) {
+ fail = true;
+ put_page(virt_to_page(args->sb_disk));
+ blkdev_put(args->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+ goto out;
+ }
+
+ /* blkdev_put() will be called in bch_cache_release() */
+ if (register_cache(args->sb, args->sb_disk, args->bdev, ca) != 0)
+ fail = true;
+
+out:
+ if (fail)
+ pr_info("error %s: fail to register cache device\n",
+ args->path);
+ kfree(args->sb);
+ kfree(args->path);
+ kfree(args);
+ module_put(THIS_MODULE);
+}
+
+static void register_device_aync(struct async_reg_args *args)
+{
+ if (SB_IS_BDEV(args->sb))
+ INIT_WORK(&args->reg_work, register_bdev_worker);
+ else
+ INIT_WORK(&args->reg_work, register_cache_worker);
+
+ queue_work(system_wq, &args->reg_work);
+}
+
static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
const char *buffer, size_t size)
{
@@ -2424,6 +2502,26 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
goto out_blkdev_put;
err = "failed to register device";
+ if (attr == &ksysfs_register_async) {
+ /* register in asynchronous way */
+ struct async_reg_args *args =
+ kzalloc(sizeof(struct async_reg_args), GFP_KERNEL);
+
+ if (!args) {
+ ret = -ENOMEM;
+ err = "cannot allocate memory";
+ goto out_put_sb_page;
+ }
+
+ args->path = path;
+ args->sb = sb;
+ args->sb_disk = sb_disk;
+ args->bdev = bdev;
+ register_device_aync(args);
+ /* No wait and returns to user space */
+ goto async_done;
+ }
+
if (SB_IS_BDEV(sb)) {
struct cached_dev *dc = kzalloc(sizeof(*dc), GFP_KERNEL);
@@ -2451,6 +2549,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
kfree(sb);
kfree(path);
module_put(THIS_MODULE);
+async_done:
return size;
out_put_sb_page:
@@ -2666,6 +2765,7 @@ static int __init bcache_init(void)
static const struct attribute *files[] = {
&ksysfs_register.attr,
&ksysfs_register_quiet.attr,
+ &ksysfs_register_async.attr,
&ksysfs_pendings_cleanup.attr,
NULL
};
When there is a lot of data cached on cache device, the bcach internal btree can take a very long to validate during the backing device and cache device registration. In my test, it may takes 55+ minutes to check all the internal btree nodes. The problem is that the registration is invoked by udev rules and the udevd has 180 seconds timeout by default. If the btree node checking time is longer than udevd timeout, the registering process will be killed by udevd with SIGKILL. If the registering process has pending sigal, creating kthread for bcache will fail and the device registration will fail. The result is, for bcache device which cached a lot of data on cache device, the bcache device node like /dev/bcache<N> won't create always due to the very long btree checking time. A solution to avoid the udevd 180 seconds timeout is to register devices in an asynchronous way. Which is, after writing cache or backing device path into /sys/fs/bcache/register_async, the kernel code will create a kworker and move all the btree node checking (for cache device) or dirty data counting (for cached device) in the kwork context. Then the kworder is scheduled on system_wq and the registration code just returned to user space udev rule task. By this asynchronous way, the udev task for bcache rule will complete in seconds, no matter how long time spent in the kworker context, it won't be killed by udevd for a timeout. After all the checking and counting are done asynchronously in the kworker, the bcache device will eventually be created successfully. This patch does the above chagne and add a register sysfs file /sys/fs/bcache/register_async. Writing the registering device path into this sysfs file will do the asynchronous registration. The register_async interface is for very rare condition and won't be used for common users. In future I plan to make the asynchronous registration as default behavior, which depends on feedback for this patch. Signed-off-by: Coly Li <colyli@suse.de> --- drivers/md/bcache/super.c | 100 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+)