From 34dd82afd27da2537199d7f71f1542501c6f96e7 Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Sun, 31 Jul 2011 22:08:04 +0200 Subject: loop: replace linked list of allocated devices with an idr index Replace the linked list, that keeps track of allocated devices, with an idr index to allow a more efficient lookup of devices. Cc: Tejun Heo Signed-off-by: Kay Sievers Signed-off-by: Jens Axboe --- drivers/block/loop.c | 152 +++++++++++++++++++++++++++------------------------ 1 file changed, 80 insertions(+), 72 deletions(-) (limited to 'drivers/block/loop.c') diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 76c8da78212b..f58532e77777 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -78,8 +78,8 @@ #include -static LIST_HEAD(loop_devices); -static DEFINE_MUTEX(loop_devices_mutex); +static DEFINE_IDR(loop_index_idr); +static DEFINE_MUTEX(loop_index_mutex); static int max_part; static int part_shift; @@ -722,17 +722,10 @@ static inline int is_loop_device(struct file *file) static ssize_t loop_attr_show(struct device *dev, char *page, ssize_t (*callback)(struct loop_device *, char *)) { - struct loop_device *l, *lo = NULL; - - mutex_lock(&loop_devices_mutex); - list_for_each_entry(l, &loop_devices, lo_list) - if (disk_to_dev(l->lo_disk) == dev) { - lo = l; - break; - } - mutex_unlock(&loop_devices_mutex); + struct gendisk *disk = dev_to_disk(dev); + struct loop_device *lo = disk->private_data; - return lo ? callback(lo, page) : -EIO; + return callback(lo, page); } #define LOOP_ATTR_RO(_name) \ @@ -1557,40 +1550,64 @@ int loop_register_transfer(struct loop_func_table *funcs) return 0; } +static int unregister_transfer_cb(int id, void *ptr, void *data) +{ + struct loop_device *lo = ptr; + struct loop_func_table *xfer = data; + + mutex_lock(&lo->lo_ctl_mutex); + if (lo->lo_encryption == xfer) + loop_release_xfer(lo); + mutex_unlock(&lo->lo_ctl_mutex); + return 0; +} + int loop_unregister_transfer(int number) { unsigned int n = number; - struct loop_device *lo; struct loop_func_table *xfer; if (n == 0 || n >= MAX_LO_CRYPT || (xfer = xfer_funcs[n]) == NULL) return -EINVAL; xfer_funcs[n] = NULL; - - list_for_each_entry(lo, &loop_devices, lo_list) { - mutex_lock(&lo->lo_ctl_mutex); - - if (lo->lo_encryption == xfer) - loop_release_xfer(lo); - - mutex_unlock(&lo->lo_ctl_mutex); - } - + idr_for_each(&loop_index_idr, &unregister_transfer_cb, xfer); return 0; } EXPORT_SYMBOL(loop_register_transfer); EXPORT_SYMBOL(loop_unregister_transfer); -static struct loop_device *loop_alloc(int i) +static int loop_add(struct loop_device **l, int i) { struct loop_device *lo; struct gendisk *disk; + int err; lo = kzalloc(sizeof(*lo), GFP_KERNEL); - if (!lo) + if (!lo) { + err = -ENOMEM; goto out; + } + + err = idr_pre_get(&loop_index_idr, GFP_KERNEL); + if (err < 0) + goto out_free_dev; + + if (i >= 0) { + int m; + + /* create specific i in the index */ + err = idr_get_new_above(&loop_index_idr, lo, i, &m); + if (err >= 0 && i != m) { + idr_remove(&loop_index_idr, m); + err = -EEXIST; + } + } else { + err = -EINVAL; + } + if (err < 0) + goto out_free_dev; lo->lo_queue = blk_alloc_queue(GFP_KERNEL); if (!lo->lo_queue) @@ -1611,56 +1628,54 @@ static struct loop_device *loop_alloc(int i) disk->private_data = lo; disk->queue = lo->lo_queue; sprintf(disk->disk_name, "loop%d", i); - return lo; + add_disk(disk); + *l = lo; + return lo->lo_number; out_free_queue: blk_cleanup_queue(lo->lo_queue); out_free_dev: kfree(lo); out: - return NULL; + return err; } -static void loop_free(struct loop_device *lo) +static void loop_remove(struct loop_device *lo) { + del_gendisk(lo->lo_disk); blk_cleanup_queue(lo->lo_queue); put_disk(lo->lo_disk); - list_del(&lo->lo_list); kfree(lo); } -static struct loop_device *loop_init_one(int i) +static int loop_lookup(struct loop_device **l, int i) { struct loop_device *lo; + int ret = -ENODEV; - list_for_each_entry(lo, &loop_devices, lo_list) { - if (lo->lo_number == i) - return lo; - } - - lo = loop_alloc(i); + lo = idr_find(&loop_index_idr, i); if (lo) { - add_disk(lo->lo_disk); - list_add_tail(&lo->lo_list, &loop_devices); + *l = lo; + ret = lo->lo_number; } - return lo; -} - -static void loop_del_one(struct loop_device *lo) -{ - del_gendisk(lo->lo_disk); - loop_free(lo); + return ret; } static struct kobject *loop_probe(dev_t dev, int *part, void *data) { struct loop_device *lo; struct kobject *kobj; + int err; - mutex_lock(&loop_devices_mutex); - lo = loop_init_one(MINOR(dev) >> part_shift); - kobj = lo ? get_disk(lo->lo_disk) : ERR_PTR(-ENOMEM); - mutex_unlock(&loop_devices_mutex); + mutex_lock(&loop_index_mutex); + err = loop_lookup(&lo, MINOR(dev) >> part_shift); + if (err < 0) + err = loop_add(&lo, MINOR(dev) >> part_shift); + if (err < 0) + kobj = ERR_PTR(err); + else + kobj = get_disk(lo->lo_disk); + mutex_unlock(&loop_index_mutex); *part = 0; return kobj; @@ -1670,7 +1685,7 @@ static int __init loop_init(void) { int i, nr; unsigned long range; - struct loop_device *lo, *next; + struct loop_device *lo; /* * loop module now has a feature to instantiate underlying device @@ -1719,43 +1734,36 @@ static int __init loop_init(void) if (register_blkdev(LOOP_MAJOR, "loop")) return -EIO; - for (i = 0; i < nr; i++) { - lo = loop_alloc(i); - if (!lo) - goto Enomem; - list_add_tail(&lo->lo_list, &loop_devices); - } - - /* point of no return */ - - list_for_each_entry(lo, &loop_devices, lo_list) - add_disk(lo->lo_disk); - blk_register_region(MKDEV(LOOP_MAJOR, 0), range, THIS_MODULE, loop_probe, NULL, NULL); + /* pre-create number devices of devices given by config or max_loop */ + mutex_lock(&loop_index_mutex); + for (i = 0; i < nr; i++) + loop_add(&lo, i); + mutex_unlock(&loop_index_mutex); + printk(KERN_INFO "loop: module loaded\n"); return 0; +} -Enomem: - printk(KERN_INFO "loop: out of memory\n"); - - list_for_each_entry_safe(lo, next, &loop_devices, lo_list) - loop_free(lo); +static int loop_exit_cb(int id, void *ptr, void *data) +{ + struct loop_device *lo = ptr; - unregister_blkdev(LOOP_MAJOR, "loop"); - return -ENOMEM; + loop_remove(lo); + return 0; } static void __exit loop_exit(void) { unsigned long range; - struct loop_device *lo, *next; range = max_loop ? max_loop << part_shift : 1UL << MINORBITS; - list_for_each_entry_safe(lo, next, &loop_devices, lo_list) - loop_del_one(lo); + idr_for_each(&loop_index_idr, &loop_exit_cb, NULL); + idr_remove_all(&loop_index_idr); + idr_destroy(&loop_index_idr); blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range); unregister_blkdev(LOOP_MAJOR, "loop"); -- cgit v1.2.3 From 770fe30a46a12b6fb6b63fbe1737654d28e84844 Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Sun, 31 Jul 2011 22:08:04 +0200 Subject: loop: add management interface for on-demand device allocation Loop devices today have a fixed pre-allocated number of usually 8. The number can only be changed at module init time. To find a free device to use, /dev/loop%i needs to be scanned, and all devices need to be opened until a free one is possibly found. This adds a new /dev/loop-control device node, that allows to dynamically find or allocate a free device, and to add and remove loop devices from the running system: LOOP_CTL_ADD adds a specific device. Arg is the number of the device. It returns the device i or a negative error code. LOOP_CTL_REMOVE removes a specific device, Arg is the number the device. It returns the device i or a negative error code. LOOP_CTL_GET_FREE finds the next unbound device or allocates a new one. No arg is given. It returns the device i or a negative error code. The loop kernel module gets automatically loaded when /dev/loop-control is accessed the first time. The alias specified in the module, instructs udev to create this 'dead' device node, even when the module is not loaded. Example: cfd = open("/dev/loop-control", O_RDWR); # add a new specific loop device err = ioctl(cfd, LOOP_CTL_ADD, devnr); # remove a specific loop device err = ioctl(cfd, LOOP_CTL_REMOVE, devnr); # find or allocate a free loop device to use devnr = ioctl(cfd, LOOP_CTL_GET_FREE); sprintf(loopname, "/dev/loop%i", devnr); ffd = open("backing-file", O_RDWR); lfd = open(loopname, O_RDWR); err = ioctl(lfd, LOOP_SET_FD, ffd); Cc: Tejun Heo Cc: Karel Zak Signed-off-by: Kay Sievers Signed-off-by: Jens Axboe --- drivers/block/loop.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 116 insertions(+), 4 deletions(-) (limited to 'drivers/block/loop.c') diff --git a/drivers/block/loop.c b/drivers/block/loop.c index f58532e77777..5c9edf944879 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -75,7 +75,7 @@ #include #include #include - +#include #include static DEFINE_IDR(loop_index_idr); @@ -1478,13 +1478,22 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode, static int lo_open(struct block_device *bdev, fmode_t mode) { - struct loop_device *lo = bdev->bd_disk->private_data; + struct loop_device *lo; + int err = 0; + + mutex_lock(&loop_index_mutex); + lo = bdev->bd_disk->private_data; + if (!lo) { + err = -ENXIO; + goto out; + } mutex_lock(&lo->lo_ctl_mutex); lo->lo_refcnt++; mutex_unlock(&lo->lo_ctl_mutex); - - return 0; +out: + mutex_unlock(&loop_index_mutex); + return err; } static int lo_release(struct gendisk *disk, fmode_t mode) @@ -1603,6 +1612,13 @@ static int loop_add(struct loop_device **l, int i) idr_remove(&loop_index_idr, m); err = -EEXIST; } + } else if (i == -1) { + int m; + + /* get next free nr */ + err = idr_get_new(&loop_index_idr, lo, &m); + if (err >= 0) + i = m; } else { err = -EINVAL; } @@ -1648,16 +1664,41 @@ static void loop_remove(struct loop_device *lo) kfree(lo); } +static int find_free_cb(int id, void *ptr, void *data) +{ + struct loop_device *lo = ptr; + struct loop_device **l = data; + + if (lo->lo_state == Lo_unbound) { + *l = lo; + return 1; + } + return 0; +} + static int loop_lookup(struct loop_device **l, int i) { struct loop_device *lo; int ret = -ENODEV; + if (i < 0) { + int err; + + err = idr_for_each(&loop_index_idr, &find_free_cb, &lo); + if (err == 1) { + *l = lo; + ret = lo->lo_number; + } + goto out; + } + + /* lookup and return a specific i */ lo = idr_find(&loop_index_idr, i); if (lo) { *l = lo; ret = lo->lo_number; } +out: return ret; } @@ -1681,11 +1722,76 @@ static struct kobject *loop_probe(dev_t dev, int *part, void *data) return kobj; } +static long loop_control_ioctl(struct file *file, unsigned int cmd, + unsigned long parm) +{ + struct loop_device *lo; + int ret = -ENOSYS; + + mutex_lock(&loop_index_mutex); + switch (cmd) { + case LOOP_CTL_ADD: + ret = loop_lookup(&lo, parm); + if (ret >= 0) { + ret = -EEXIST; + break; + } + ret = loop_add(&lo, parm); + break; + case LOOP_CTL_REMOVE: + ret = loop_lookup(&lo, parm); + if (ret < 0) + break; + mutex_lock(&lo->lo_ctl_mutex); + if (lo->lo_state != Lo_unbound) { + ret = -EBUSY; + mutex_unlock(&lo->lo_ctl_mutex); + break; + } + if (lo->lo_refcnt > 0) { + ret = -EBUSY; + mutex_unlock(&lo->lo_ctl_mutex); + break; + } + lo->lo_disk->private_data = NULL; + mutex_unlock(&lo->lo_ctl_mutex); + idr_remove(&loop_index_idr, lo->lo_number); + loop_remove(lo); + break; + case LOOP_CTL_GET_FREE: + ret = loop_lookup(&lo, -1); + if (ret >= 0) + break; + ret = loop_add(&lo, -1); + } + mutex_unlock(&loop_index_mutex); + + return ret; +} + +static const struct file_operations loop_ctl_fops = { + .open = nonseekable_open, + .unlocked_ioctl = loop_control_ioctl, + .compat_ioctl = loop_control_ioctl, + .owner = THIS_MODULE, + .llseek = noop_llseek, +}; + +static struct miscdevice loop_misc = { + .minor = LOOP_CTRL_MINOR, + .name = "loop-control", + .fops = &loop_ctl_fops, +}; + +MODULE_ALIAS_MISCDEV(LOOP_CTRL_MINOR); +MODULE_ALIAS("devname:loop-control"); + static int __init loop_init(void) { int i, nr; unsigned long range; struct loop_device *lo; + int err; /* * loop module now has a feature to instantiate underlying device @@ -1702,6 +1808,10 @@ static int __init loop_init(void) * device on-demand. */ + err = misc_register(&loop_misc); + if (err < 0) + return err; + part_shift = 0; if (max_part > 0) { part_shift = fls(max_part); @@ -1767,6 +1877,8 @@ static void __exit loop_exit(void) blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range); unregister_blkdev(LOOP_MAJOR, "loop"); + + misc_deregister(&loop_misc); } module_init(loop_init); -- cgit v1.2.3 From d134b00b9acca3fb054d7c88a5f5d562ecbb42d1 Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Sun, 31 Jul 2011 22:08:04 +0200 Subject: loop: add BLK_DEV_LOOP_MIN_COUNT=%i to allow distros 0 pre-allocated loop devices Instead of unconditionally creating a fixed number of dead loop devices which need to be investigated by storage handling services, even when they are never used, we allow distros start with 0 loop devices and have losetup(8) and similar switch to the dynamic /dev/loop-control interface instead of searching /dev/loop%i for free devices. Signed-off-by: Kay Sievers Signed-off-by: Jens Axboe --- drivers/block/loop.c | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-) (limited to 'drivers/block/loop.c') diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 5c9edf944879..3defc52f060c 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1793,21 +1793,6 @@ static int __init loop_init(void) struct loop_device *lo; int err; - /* - * loop module now has a feature to instantiate underlying device - * structure on-demand, provided that there is an access dev node. - * However, this will not work well with user space tool that doesn't - * know about such "feature". In order to not break any existing - * tool, we do the following: - * - * (1) if max_loop is specified, create that many upfront, and this - * also becomes a hard limit. - * (2) if max_loop is not specified, create 8 loop device on module - * load, user can further extend loop device by create dev node - * themselves and have kernel automatically instantiate actual - * device on-demand. - */ - err = misc_register(&loop_misc); if (err < 0) return err; @@ -1833,11 +1818,19 @@ static int __init loop_init(void) if (max_loop > 1UL << (MINORBITS - part_shift)) return -EINVAL; + /* + * If max_loop is specified, create that many devices upfront. + * This also becomes a hard limit. If max_loop is not specified, + * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module + * init time. Loop devices can be requested on-demand with the + * /dev/loop-control interface, or be instantiated by accessing + * a 'dead' device node. + */ if (max_loop) { nr = max_loop; range = max_loop << part_shift; } else { - nr = 8; + nr = CONFIG_BLK_DEV_LOOP_MIN_COUNT; range = 1UL << MINORBITS; } @@ -1847,7 +1840,7 @@ static int __init loop_init(void) blk_register_region(MKDEV(LOOP_MAJOR, 0), range, THIS_MODULE, loop_probe, NULL, NULL); - /* pre-create number devices of devices given by config or max_loop */ + /* pre-create number of devices given by config or max_loop */ mutex_lock(&loop_index_mutex); for (i = 0; i < nr; i++) loop_add(&lo, i); -- cgit v1.2.3 From 05eb0f252b04aa94ace0794f73d56c6a02351d80 Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Sun, 31 Jul 2011 22:21:35 +0200 Subject: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other LOOP_CLR_FD takes lo->lo_ctl_mutex and tries to remove the loop sysfs files. Sysfs calls show() and waits for lo->lo_ctl_mutex. LOOP_CLR_FD waits for show() to finish to remove the sysfs file. cat /sys/class/block/loop0/loop/backing_file mutex_lock_nested+0x176/0x350 ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop] ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop] loop_attr_do_show_backing_file+0x2f/0xd0 [loop] dev_attr_show+0x1b/0x60 ? sysfs_read_file+0x86/0x1a0 ? __get_free_pages+0x12/0x50 sysfs_read_file+0xaf/0x1a0 ioctl(LOOP_CLR_FD): wait_for_common+0x12c/0x180 ? try_to_wake_up+0x2a0/0x2a0 wait_for_completion+0x18/0x20 sysfs_deactivate+0x178/0x180 ? sysfs_addrm_finish+0x43/0x70 ? sysfs_addrm_start+0x1d/0x20 sysfs_addrm_finish+0x43/0x70 sysfs_hash_and_remove+0x85/0xa0 sysfs_remove_group+0x59/0x100 loop_clr_fd+0x1dc/0x3f0 [loop] lo_ioctl+0x223/0x7a0 [loop] Instead of taking the lo_ctl_mutex from sysfs code, take the inner lo->lo_lock, to protect the access to the backing_file data. Thanks to Tejun for help debugging and finding a solution. Cc: Milan Broz Cc: Tejun Heo Signed-off-by: Kay Sievers Cc: stable@kernel.org Signed-off-by: Jens Axboe --- drivers/block/loop.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'drivers/block/loop.c') diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 3defc52f060c..4720c7ade0ae 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -743,10 +743,10 @@ static ssize_t loop_attr_backing_file_show(struct loop_device *lo, char *buf) ssize_t ret; char *p = NULL; - mutex_lock(&lo->lo_ctl_mutex); + spin_lock_irq(&lo->lo_lock); if (lo->lo_backing_file) p = d_path(&lo->lo_backing_file->f_path, buf, PAGE_SIZE - 1); - mutex_unlock(&lo->lo_ctl_mutex); + spin_unlock_irq(&lo->lo_lock); if (IS_ERR_OR_NULL(p)) ret = PTR_ERR(p); @@ -1000,7 +1000,9 @@ static int loop_clr_fd(struct loop_device *lo, struct block_device *bdev) kthread_stop(lo->lo_thread); + spin_lock_irq(&lo->lo_lock); lo->lo_backing_file = NULL; + spin_unlock_irq(&lo->lo_lock); loop_release_xfer(lo); lo->transfer = NULL; -- cgit v1.2.3