diff options
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/md/Kconfig | 4 | ||||
| -rw-r--r-- | drivers/md/Makefile | 1 | ||||
| -rw-r--r-- | drivers/md/dm-builtin.c | 48 | ||||
| -rw-r--r-- | drivers/md/dm-sysfs.c | 5 | ||||
| -rw-r--r-- | drivers/md/dm.c | 20 | ||||
| -rw-r--r-- | drivers/md/dm.h | 17 |
6 files changed, 74 insertions, 21 deletions
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig index 39b540a13369..9a06fe883766 100644 --- a/drivers/md/Kconfig +++ b/drivers/md/Kconfig @@ -176,8 +176,12 @@ config MD_FAULTY source "drivers/md/bcache/Kconfig" +config BLK_DEV_DM_BUILTIN + boolean + config BLK_DEV_DM tristate "Device mapper support" + select BLK_DEV_DM_BUILTIN ---help--- Device-mapper is a low level volume manager. It works by allowing people to specify mappings for ranges of logical sectors. Various diff --git a/drivers/md/Makefile b/drivers/md/Makefile index 2acc43fe0229..f26d83292579 100644 --- a/drivers/md/Makefile +++ b/drivers/md/Makefile @@ -32,6 +32,7 @@ obj-$(CONFIG_MD_FAULTY) += faulty.o obj-$(CONFIG_BCACHE) += bcache/ obj-$(CONFIG_BLK_DEV_MD) += md-mod.o obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o +obj-$(CONFIG_BLK_DEV_DM_BUILTIN) += dm-builtin.o obj-$(CONFIG_DM_BUFIO) += dm-bufio.o obj-$(CONFIG_DM_BIO_PRISON) += dm-bio-prison.o obj-$(CONFIG_DM_CRYPT) += dm-crypt.o diff --git a/drivers/md/dm-builtin.c b/drivers/md/dm-builtin.c new file mode 100644 index 000000000000..6c9049c51b2b --- /dev/null +++ b/drivers/md/dm-builtin.c @@ -0,0 +1,48 @@ +#include "dm.h" + +/* + * The kobject release method must not be placed in the module itself, + * otherwise we are subject to module unload races. + * + * The release method is called when the last reference to the kobject is + * dropped. It may be called by any other kernel code that drops the last + * reference. + * + * The release method suffers from module unload race. We may prevent the + * module from being unloaded at the start of the release method (using + * increased module reference count or synchronizing against the release + * method), however there is no way to prevent the module from being + * unloaded at the end of the release method. + * + * If this code were placed in the dm module, the following race may + * happen: + * 1. Some other process takes a reference to dm kobject + * 2. The user issues ioctl function to unload the dm device + * 3. dm_sysfs_exit calls kobject_put, however the object is not released + * because of the other reference taken at step 1 + * 4. dm_sysfs_exit waits on the completion + * 5. The other process that took the reference in step 1 drops it, + * dm_kobject_release is called from this process + * 6. dm_kobject_release calls complete() + * 7. a reschedule happens before dm_kobject_release returns + * 8. dm_sysfs_exit continues, the dm device is unloaded, module reference + * count is decremented + * 9. The user unloads the dm module + * 10. The other process that was rescheduled in step 7 continues to run, + * it is now executing code in unloaded module, so it crashes + * + * Note that if the process that takes the foreign reference to dm kobject + * has a low priority and the system is sufficiently loaded with + * higher-priority processes that prevent the low-priority process from + * being scheduled long enough, this bug may really happen. + * + * In order to fix this module unload race, we place the release method + * into a helper code that is compiled directly into the kernel. + */ + +void dm_kobject_release(struct kobject *kobj) +{ + complete(dm_get_completion_from_kobject(kobj)); +} + +EXPORT_SYMBOL(dm_kobject_release); diff --git a/drivers/md/dm-sysfs.c b/drivers/md/dm-sysfs.c index e0cc5d6a9e46..c62c5ab6aed5 100644 --- a/drivers/md/dm-sysfs.c +++ b/drivers/md/dm-sysfs.c @@ -79,11 +79,6 @@ static const struct sysfs_ops dm_sysfs_ops = { .show = dm_attr_show, }; -static void dm_kobject_release(struct kobject *kobj) -{ - complete(dm_get_completion_from_kobject(kobj)); -} - /* * dm kobject is embedded in mapped_device structure * no need to define release function here diff --git a/drivers/md/dm.c b/drivers/md/dm.c index e290e72922a4..b49c76284241 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -200,11 +200,8 @@ struct mapped_device { /* forced geometry settings */ struct hd_geometry geometry; - /* sysfs handle */ - struct kobject kobj; - - /* wait until the kobject is released */ - struct completion kobj_completion; + /* kobject and completion */ + struct dm_kobject_holder kobj_holder; /* zero-length flush that will be cloned and submitted to targets */ struct bio flush_bio; @@ -2044,7 +2041,7 @@ static struct mapped_device *alloc_dev(int minor) init_waitqueue_head(&md->wait); INIT_WORK(&md->work, dm_wq_work); init_waitqueue_head(&md->eventq); - init_completion(&md->kobj_completion); + init_completion(&md->kobj_holder.completion); md->disk->major = _major; md->disk->first_minor = minor; @@ -2906,14 +2903,14 @@ struct gendisk *dm_disk(struct mapped_device *md) struct kobject *dm_kobject(struct mapped_device *md) { - return &md->kobj; + return &md->kobj_holder.kobj; } struct mapped_device *dm_get_from_kobject(struct kobject *kobj) { struct mapped_device *md; - md = container_of(kobj, struct mapped_device, kobj); + md = container_of(kobj, struct mapped_device, kobj_holder.kobj); if (test_bit(DMF_FREEING, &md->flags) || dm_deleting_md(md)) @@ -2923,13 +2920,6 @@ struct mapped_device *dm_get_from_kobject(struct kobject *kobj) return md; } -struct completion *dm_get_completion_from_kobject(struct kobject *kobj) -{ - struct mapped_device *md = container_of(kobj, struct mapped_device, kobj); - - return &md->kobj_completion; -} - int dm_suspended_md(struct mapped_device *md) { return test_bit(DMF_SUSPENDED, &md->flags); diff --git a/drivers/md/dm.h b/drivers/md/dm.h index 1ab2028559ca..c4569f02f50f 100644 --- a/drivers/md/dm.h +++ b/drivers/md/dm.h @@ -16,6 +16,7 @@ #include <linux/blkdev.h> #include <linux/hdreg.h> #include <linux/completion.h> +#include <linux/kobject.h> #include "dm-stats.h" @@ -149,11 +150,25 @@ void dm_interface_exit(void); /* * sysfs interface */ +struct dm_kobject_holder { + struct kobject kobj; + struct completion completion; +}; + +static inline struct completion *dm_get_completion_from_kobject(struct kobject *kobj) +{ + return &container_of(kobj, struct dm_kobject_holder, kobj)->completion; +} + int dm_sysfs_init(struct mapped_device *md); void dm_sysfs_exit(struct mapped_device *md); struct kobject *dm_kobject(struct mapped_device *md); struct mapped_device *dm_get_from_kobject(struct kobject *kobj); -struct completion *dm_get_completion_from_kobject(struct kobject *kobj); + +/* + * The kobject helper + */ +void dm_kobject_release(struct kobject *kobj); /* * Targets for linear and striped mappings |