On Mon, 10 Feb 2014, Greg KH wrote:
> On Mon, Feb 10, 2014 at 03:02:24PM -0500, Mikulas Patocka wrote: > > > > > > On Sat, 8 Feb 2014, [email protected] wrote: > > > > > The patch below does not apply to the 3.13-stable tree. > > > If someone wants it applied there, or to any other stable or longterm > > > tree, then please email the backport, including the original git commit > > > id to <[email protected]>. > > > > > > thanks, > > > > > > greg k-h > > > > Hi > > > > Here I'm sending backported patch > > 2995fa78e423d7193f3b57835f6c1c75006a0315. It applies to stable kernels > > 3.4 - 3.13 (and maybe also on older versions). > > For 3.10-3.13 this patch works, but for 3.4 I get the build error: > > ERROR: "dm_kobject_release" [drivers/md/dm-mod.ko] undefined! > /ssd/gregkh-linux/stable/linux-3.4.y/scripts/Makefile.modpost:91: recipe for > target '__modpost' failed > make[1]: *** [__modpost] Error 1 > > So I'm dropping it from that branch. Care to send me a version that > builds properly for that kernel release? > > thanks, > > greg k-h This is the update of 2995fa78e423d7193f3b57835f6c1c75006a0315 for stable 3.4. Mikulas From: Mikulas Patocka <[email protected]> commit 2995fa78e423d7193f3b57835f6c1c75006a0315 Author: Mikulas Patocka <[email protected]> Date: Mon Jan 13 19:37:54 2014 -0500 dm sysfs: fix a module unload race This reverts commit be35f48610 ("dm: wait until embedded kobject is released before destroying a device") and provides an improved fix. The kobject release code that calls the completion must be placed in a non-module file, otherwise there is a module unload race (if the process calling dm_kobject_release is preempted and the DM module unloaded after the completion is triggered, but before dm_kobject_release returns). To fix this race, this patch moves the completion code to dm-builtin.c which is always compiled directly into the kernel if BLK_DEV_DM is selected. The patch introduces a new dm_kobject_holder structure, its purpose is to keep the completion and kobject in one place, so that it can be accessed from non-module code without the need to export the layout of struct mapped_device to that code. Signed-off-by: Mikulas Patocka <[email protected]> Signed-off-by: Mike Snitzer <[email protected]> Cc: [email protected] --- drivers/md/Kconfig | 4 +++ drivers/md/Makefile | 1 drivers/md/dm-builtin.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++ drivers/md/dm-sysfs.c | 5 ---- drivers/md/dm.c | 26 ++++-------------------- drivers/md/dm.h | 17 +++++++++++++++- 6 files changed, 76 insertions(+), 27 deletions(-) Index: linux-stable/drivers/md/dm.c =================================================================== --- linux-stable.orig/drivers/md/dm.c 2014-02-13 15:50:13.000000000 +0100 +++ linux-stable/drivers/md/dm.c 2014-02-13 15:50:39.000000000 +0100 @@ -191,11 +191,8 @@ 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; @@ -1894,7 +1891,7 @@ static struct mapped_device *alloc_dev(i 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; @@ -2686,20 +2683,14 @@ struct gendisk *dm_disk(struct mapped_de struct kobject *dm_kobject(struct mapped_device *md) { - return &md->kobj; + return &md->kobj_holder.kobj; } -/* - * struct mapped_device should not be exported outside of dm.c - * so use this check to verify that kobj is part of md structure - */ struct mapped_device *dm_get_from_kobject(struct kobject *kobj) { struct mapped_device *md; - md = container_of(kobj, struct mapped_device, kobj); - if (&md->kobj != kobj) - return NULL; + md = container_of(kobj, struct mapped_device, kobj_holder.kobj); if (test_bit(DMF_FREEING, &md->flags) || dm_deleting_md(md)) @@ -2709,13 +2700,6 @@ struct mapped_device *dm_get_from_kobjec 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); Index: linux-stable/drivers/md/Kconfig =================================================================== --- linux-stable.orig/drivers/md/Kconfig 2014-02-11 00:01:38.000000000 +0100 +++ linux-stable/drivers/md/Kconfig 2014-02-13 15:50:39.000000000 +0100 @@ -185,8 +185,12 @@ config MD_FAULTY In unsure, say N. +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 Index: linux-stable/drivers/md/Makefile =================================================================== --- linux-stable.orig/drivers/md/Makefile 2014-02-11 00:01:38.000000000 +0100 +++ linux-stable/drivers/md/Makefile 2014-02-13 15:50:39.000000000 +0100 @@ -28,6 +28,7 @@ obj-$(CONFIG_MD_MULTIPATH) += multipath. obj-$(CONFIG_MD_FAULTY) += faulty.o 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-$(CONFIG_DM_CRYPT) += dm-crypt.o obj-$(CONFIG_DM_DELAY) += dm-delay.o Index: linux-stable/drivers/md/dm-builtin.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-stable/drivers/md/dm-builtin.c 2014-02-13 16:05:16.000000000 +0100 @@ -0,0 +1,50 @@ +#include "dm.h" + +#include <linux/export.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); Index: linux-stable/drivers/md/dm-sysfs.c =================================================================== --- linux-stable.orig/drivers/md/dm-sysfs.c 2014-02-13 15:50:13.000000000 +0100 +++ linux-stable/drivers/md/dm-sysfs.c 2014-02-13 15:50:39.000000000 +0100 @@ -79,11 +79,6 @@ static const struct sysfs_ops dm_sysfs_o .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 Index: linux-stable/drivers/md/dm.h =================================================================== --- linux-stable.orig/drivers/md/dm.h 2014-02-13 15:50:13.000000000 +0100 +++ linux-stable/drivers/md/dm.h 2014-02-13 15:50:39.000000000 +0100 @@ -16,6 +16,7 @@ #include <linux/blkdev.h> #include <linux/hdreg.h> #include <linux/completion.h> +#include <linux/kobject.h> /* * Suspend feature flags @@ -120,11 +121,25 @@ 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
