| Message ID | 20190524135738.54862-4-parav@mellanox.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio/mdev: Improve vfio/mdev core module | expand |
On Fri, 24 May 2019 08:57:38 -0500 Parav Pandit <parav@mellanox.com> wrote: > In following sequences, child devices created while removing mdev parent > device can be left out, or it may lead to race of removing half > initialized child mdev devices. > > issue-1: > -------- > cpu-0 cpu-1 > ----- ----- > mdev_unregister_device() > device_for_each_child() > mdev_device_remove_cb() > mdev_device_remove() > create_store() > mdev_device_create() [...] > device_add() > parent_remove_sysfs_files() > > /* BUG: device added by cpu-0 > * whose parent is getting removed > * and it won't process this mdev. > */ > > issue-2: > -------- > Below crash is observed when user initiated remove is in progress > and mdev_unregister_driver() completes parent unregistration. > > cpu-0 cpu-1 > ----- ----- > remove_store() > mdev_device_remove() > active = false; > mdev_unregister_device() > parent device removed. > [...] > parents->ops->remove() > /* > * BUG: Accessing invalid parent. > */ > > This is similar race like create() racing with mdev_unregister_device(). > > BUG: unable to handle kernel paging request at ffffffffc0585668 > PGD e8f618067 P4D e8f618067 PUD e8f61a067 PMD 85adca067 PTE 0 > Oops: 0000 [#1] SMP PTI > CPU: 41 PID: 37403 Comm: bash Kdump: loaded Not tainted 5.1.0-rc6-vdevbus+ #6 > Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b 08/09/2016 > RIP: 0010:mdev_device_remove+0xfa/0x140 [mdev] > Call Trace: > remove_store+0x71/0x90 [mdev] > kernfs_fop_write+0x113/0x1a0 > vfs_write+0xad/0x1b0 > ksys_write+0x5a/0xe0 > do_syscall_64+0x5a/0x210 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Therefore, mdev core is improved as below to overcome above issues. > > Wait for any ongoing mdev create() and remove() to finish before > unregistering parent device. > This continues to allow multiple create and remove to progress in > parallel for different mdev devices as most common case. > At the same time guard parent removal while parent is being access by > create() and remove callbacks. > create()/remove() and unregister_device() are synchronized by the rwsem. > > Refactor device removal code to mdev_device_remove_common() to avoid > acquiring unreg_sem of the parent. > > Fixes: 7b96953bc640 ("vfio: Mediated device Core driver") > Signed-off-by: Parav Pandit <parav@mellanox.com> > --- > drivers/vfio/mdev/mdev_core.c | 61 ++++++++++++++++++++++++-------- > drivers/vfio/mdev/mdev_private.h | 2 ++ > 2 files changed, 49 insertions(+), 14 deletions(-) > > diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c > index 0bef0cae1d4b..c5401a8c6843 100644 > --- a/drivers/vfio/mdev/mdev_core.c > +++ b/drivers/vfio/mdev/mdev_core.c > @@ -102,11 +102,36 @@ static void mdev_put_parent(struct mdev_parent *parent) > kref_put(&parent->ref, mdev_release_parent); > } > Some sort of locking semantics comment would be useful here, ex: /* Caller holds parent unreg_sem read or write lock */ > +static void mdev_device_remove_common(struct mdev_device *mdev) > +{ > + struct mdev_parent *parent; > + struct mdev_type *type; > + int ret; > + > + type = to_mdev_type(mdev->type_kobj); > + mdev_remove_sysfs_files(&mdev->dev, type); > + device_del(&mdev->dev); > + parent = mdev->parent; > + ret = parent->ops->remove(mdev); > + if (ret) > + dev_err(&mdev->dev, "Remove failed: err=%d\n", ret); > + > + /* Balances with device_initialize() */ > + put_device(&mdev->dev); > + mdev_put_parent(parent); > +} > + > static int mdev_device_remove_cb(struct device *dev, void *data) > { > - if (dev_is_mdev(dev)) > - mdev_device_remove(dev); > + struct mdev_parent *parent; > + struct mdev_device *mdev; > > + if (!dev_is_mdev(dev)) > + return 0; > + > + mdev = to_mdev_device(dev); > + parent = mdev->parent; > + mdev_device_remove_common(mdev); 'parent' is unused here and we only use mdev once, so we probably don't need to put it in a local variable. > return 0; > } > > @@ -148,6 +173,7 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops) > } > > kref_init(&parent->ref); > + init_rwsem(&parent->unreg_sem); > > parent->dev = dev; > parent->ops = ops; > @@ -206,13 +232,17 @@ void mdev_unregister_device(struct device *dev) > dev_info(dev, "MDEV: Unregistering\n"); > > list_del(&parent->next); > + mutex_unlock(&parent_list_lock); > + > + down_write(&parent->unreg_sem); > + > class_compat_remove_link(mdev_bus_compat_class, dev, NULL); > > device_for_each_child(dev, NULL, mdev_device_remove_cb); > > parent_remove_sysfs_files(parent); > + up_write(&parent->unreg_sem); > > - mutex_unlock(&parent_list_lock); > mdev_put_parent(parent); > } > EXPORT_SYMBOL(mdev_unregister_device); > @@ -265,6 +295,12 @@ int mdev_device_create(struct kobject *kobj, > > mdev->parent = parent; > > + ret = down_read_trylock(&parent->unreg_sem); > + if (!ret) { > + ret = -ENODEV; I would have expected -EAGAIN or -EBUSY here, but I guess that since we consider the lock-out to deterministically be the parent going away that -ENODEV makes sense. Ok. > + goto mdev_fail; > + } > + > device_initialize(&mdev->dev); > mdev->dev.parent = dev; > mdev->dev.bus = &mdev_bus_type; > @@ -287,6 +323,7 @@ int mdev_device_create(struct kobject *kobj, > > mdev->active = true; > dev_dbg(&mdev->dev, "MDEV: created\n"); > + up_read(&parent->unreg_sem); > > return 0; > > @@ -295,6 +332,7 @@ int mdev_device_create(struct kobject *kobj, > add_fail: > parent->ops->remove(mdev); > ops_create_fail: > + up_read(&parent->unreg_sem); > put_device(&mdev->dev); > mdev_fail: > mdev_put_parent(parent); > @@ -305,7 +343,6 @@ int mdev_device_remove(struct device *dev) > { > struct mdev_device *mdev, *tmp; > struct mdev_parent *parent; > - struct mdev_type *type; > int ret; > > mdev = to_mdev_device(dev); > @@ -329,18 +366,14 @@ int mdev_device_remove(struct device *dev) > mdev->active = false; > mutex_unlock(&mdev_list_lock); > > - type = to_mdev_type(mdev->type_kobj); > - mdev_remove_sysfs_files(dev, type); > - device_del(&mdev->dev); > parent = mdev->parent; > - ret = parent->ops->remove(mdev); > - if (ret) > - dev_err(&mdev->dev, "Remove failed: err=%d\n", ret); > - > - /* Balances with device_initialize() */ > - put_device(&mdev->dev); > - mdev_put_parent(parent); > + /* Check if parent unregistration has started */ > + ret = down_read_trylock(&parent->unreg_sem); > + if (!ret) > + return -ENODEV; > > + mdev_device_remove_common(mdev); > + up_read(&parent->unreg_sem); > return 0; > } > > diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h > index 924ed2274941..398767526276 100644 > --- a/drivers/vfio/mdev/mdev_private.h > +++ b/drivers/vfio/mdev/mdev_private.h > @@ -23,6 +23,8 @@ struct mdev_parent { > struct list_head next; > struct kset *mdev_types_kset; > struct list_head type_list; > + /* Synchronize device creation/removal with parent unregistration */ > + struct rw_semaphore unreg_sem; > }; > > struct mdev_device {
Hi Alex, > -----Original Message----- > From: Alex Williamson <alex.williamson@redhat.com> > Sent: Wednesday, May 29, 2019 8:27 PM [..] > > > > diff --git a/drivers/vfio/mdev/mdev_core.c > > b/drivers/vfio/mdev/mdev_core.c index 0bef0cae1d4b..c5401a8c6843 > > 100644 > > --- a/drivers/vfio/mdev/mdev_core.c > > +++ b/drivers/vfio/mdev/mdev_core.c > > @@ -102,11 +102,36 @@ static void mdev_put_parent(struct mdev_parent > *parent) > > kref_put(&parent->ref, mdev_release_parent); } > > > > Some sort of locking semantics comment would be useful here, ex: > > /* Caller holds parent unreg_sem read or write lock */ > Added. > > + > > static int mdev_device_remove_cb(struct device *dev, void *data) { > > - if (dev_is_mdev(dev)) > > - mdev_device_remove(dev); > > + struct mdev_parent *parent; > > + struct mdev_device *mdev; > > > > + if (!dev_is_mdev(dev)) > > + return 0; > > + > > + mdev = to_mdev_device(dev); > > + parent = mdev->parent; > > + mdev_device_remove_common(mdev); > > 'parent' is unused here and we only use mdev once, so we probably don't need > to put it in a local variable. > Right left out from previous code. Removed and refactored the code now. > > return 0; > > } > > > > @@ -148,6 +173,7 @@ int mdev_register_device(struct device *dev, const > struct mdev_parent_ops *ops) > > } > > > > kref_init(&parent->ref); > > + init_rwsem(&parent->unreg_sem); > > > > parent->dev = dev; > > parent->ops = ops; > > @@ -206,13 +232,17 @@ void mdev_unregister_device(struct device *dev) > > dev_info(dev, "MDEV: Unregistering\n"); > > > > list_del(&parent->next); > > + mutex_unlock(&parent_list_lock); > > + > > + down_write(&parent->unreg_sem); > > + > > class_compat_remove_link(mdev_bus_compat_class, dev, NULL); > > > > device_for_each_child(dev, NULL, mdev_device_remove_cb); > > > > parent_remove_sysfs_files(parent); > > + up_write(&parent->unreg_sem); > > > > - mutex_unlock(&parent_list_lock); > > mdev_put_parent(parent); > > } > > EXPORT_SYMBOL(mdev_unregister_device); > > @@ -265,6 +295,12 @@ int mdev_device_create(struct kobject *kobj, > > > > mdev->parent = parent; > > > > + ret = down_read_trylock(&parent->unreg_sem); > > + if (!ret) { > > + ret = -ENODEV; > > I would have expected -EAGAIN or -EBUSY here, but I guess that since we > consider the lock-out to deterministically be the parent going away that - > ENODEV makes sense. Ok. > Yeah, I agree that ENODEV is more accurate error code as we don't want to tell user to retry so EAGAIN is less appropriate. Sending v5.
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c index 0bef0cae1d4b..c5401a8c6843 100644 --- a/drivers/vfio/mdev/mdev_core.c +++ b/drivers/vfio/mdev/mdev_core.c @@ -102,11 +102,36 @@ static void mdev_put_parent(struct mdev_parent *parent) kref_put(&parent->ref, mdev_release_parent); } +static void mdev_device_remove_common(struct mdev_device *mdev) +{ + struct mdev_parent *parent; + struct mdev_type *type; + int ret; + + type = to_mdev_type(mdev->type_kobj); + mdev_remove_sysfs_files(&mdev->dev, type); + device_del(&mdev->dev); + parent = mdev->parent; + ret = parent->ops->remove(mdev); + if (ret) + dev_err(&mdev->dev, "Remove failed: err=%d\n", ret); + + /* Balances with device_initialize() */ + put_device(&mdev->dev); + mdev_put_parent(parent); +} + static int mdev_device_remove_cb(struct device *dev, void *data) { - if (dev_is_mdev(dev)) - mdev_device_remove(dev); + struct mdev_parent *parent; + struct mdev_device *mdev; + if (!dev_is_mdev(dev)) + return 0; + + mdev = to_mdev_device(dev); + parent = mdev->parent; + mdev_device_remove_common(mdev); return 0; } @@ -148,6 +173,7 @@ int mdev_register_device(struct device *dev, const struct mdev_parent_ops *ops) } kref_init(&parent->ref); + init_rwsem(&parent->unreg_sem); parent->dev = dev; parent->ops = ops; @@ -206,13 +232,17 @@ void mdev_unregister_device(struct device *dev) dev_info(dev, "MDEV: Unregistering\n"); list_del(&parent->next); + mutex_unlock(&parent_list_lock); + + down_write(&parent->unreg_sem); + class_compat_remove_link(mdev_bus_compat_class, dev, NULL); device_for_each_child(dev, NULL, mdev_device_remove_cb); parent_remove_sysfs_files(parent); + up_write(&parent->unreg_sem); - mutex_unlock(&parent_list_lock); mdev_put_parent(parent); } EXPORT_SYMBOL(mdev_unregister_device); @@ -265,6 +295,12 @@ int mdev_device_create(struct kobject *kobj, mdev->parent = parent; + ret = down_read_trylock(&parent->unreg_sem); + if (!ret) { + ret = -ENODEV; + goto mdev_fail; + } + device_initialize(&mdev->dev); mdev->dev.parent = dev; mdev->dev.bus = &mdev_bus_type; @@ -287,6 +323,7 @@ int mdev_device_create(struct kobject *kobj, mdev->active = true; dev_dbg(&mdev->dev, "MDEV: created\n"); + up_read(&parent->unreg_sem); return 0; @@ -295,6 +332,7 @@ int mdev_device_create(struct kobject *kobj, add_fail: parent->ops->remove(mdev); ops_create_fail: + up_read(&parent->unreg_sem); put_device(&mdev->dev); mdev_fail: mdev_put_parent(parent); @@ -305,7 +343,6 @@ int mdev_device_remove(struct device *dev) { struct mdev_device *mdev, *tmp; struct mdev_parent *parent; - struct mdev_type *type; int ret; mdev = to_mdev_device(dev); @@ -329,18 +366,14 @@ int mdev_device_remove(struct device *dev) mdev->active = false; mutex_unlock(&mdev_list_lock); - type = to_mdev_type(mdev->type_kobj); - mdev_remove_sysfs_files(dev, type); - device_del(&mdev->dev); parent = mdev->parent; - ret = parent->ops->remove(mdev); - if (ret) - dev_err(&mdev->dev, "Remove failed: err=%d\n", ret); - - /* Balances with device_initialize() */ - put_device(&mdev->dev); - mdev_put_parent(parent); + /* Check if parent unregistration has started */ + ret = down_read_trylock(&parent->unreg_sem); + if (!ret) + return -ENODEV; + mdev_device_remove_common(mdev); + up_read(&parent->unreg_sem); return 0; } diff --git a/drivers/vfio/mdev/mdev_private.h b/drivers/vfio/mdev/mdev_private.h index 924ed2274941..398767526276 100644 --- a/drivers/vfio/mdev/mdev_private.h +++ b/drivers/vfio/mdev/mdev_private.h @@ -23,6 +23,8 @@ struct mdev_parent { struct list_head next; struct kset *mdev_types_kset; struct list_head type_list; + /* Synchronize device creation/removal with parent unregistration */ + struct rw_semaphore unreg_sem; }; struct mdev_device {
In following sequences, child devices created while removing mdev parent device can be left out, or it may lead to race of removing half initialized child mdev devices. issue-1: -------- cpu-0 cpu-1 ----- ----- mdev_unregister_device() device_for_each_child() mdev_device_remove_cb() mdev_device_remove() create_store() mdev_device_create() [...] device_add() parent_remove_sysfs_files() /* BUG: device added by cpu-0 * whose parent is getting removed * and it won't process this mdev. */ issue-2: -------- Below crash is observed when user initiated remove is in progress and mdev_unregister_driver() completes parent unregistration. cpu-0 cpu-1 ----- ----- remove_store() mdev_device_remove() active = false; mdev_unregister_device() parent device removed. [...] parents->ops->remove() /* * BUG: Accessing invalid parent. */ This is similar race like create() racing with mdev_unregister_device(). BUG: unable to handle kernel paging request at ffffffffc0585668 PGD e8f618067 P4D e8f618067 PUD e8f61a067 PMD 85adca067 PTE 0 Oops: 0000 [#1] SMP PTI CPU: 41 PID: 37403 Comm: bash Kdump: loaded Not tainted 5.1.0-rc6-vdevbus+ #6 Hardware name: Supermicro SYS-6028U-TR4+/X10DRU-i+, BIOS 2.0b 08/09/2016 RIP: 0010:mdev_device_remove+0xfa/0x140 [mdev] Call Trace: remove_store+0x71/0x90 [mdev] kernfs_fop_write+0x113/0x1a0 vfs_write+0xad/0x1b0 ksys_write+0x5a/0xe0 do_syscall_64+0x5a/0x210 entry_SYSCALL_64_after_hwframe+0x49/0xbe Therefore, mdev core is improved as below to overcome above issues. Wait for any ongoing mdev create() and remove() to finish before unregistering parent device. This continues to allow multiple create and remove to progress in parallel for different mdev devices as most common case. At the same time guard parent removal while parent is being access by create() and remove callbacks. create()/remove() and unregister_device() are synchronized by the rwsem. Refactor device removal code to mdev_device_remove_common() to avoid acquiring unreg_sem of the parent. Fixes: 7b96953bc640 ("vfio: Mediated device Core driver") Signed-off-by: Parav Pandit <parav@mellanox.com> --- drivers/vfio/mdev/mdev_core.c | 61 ++++++++++++++++++++++++-------- drivers/vfio/mdev/mdev_private.h | 2 ++ 2 files changed, 49 insertions(+), 14 deletions(-)