| Message ID | 20190603185658.54517-4-parav@mellanox.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfio/mdev: Improve vfio/mdev core module | expand |
On Mon, 3 Jun 2019 13:56:58 -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 accessed 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 | 71 ++++++++++++++++++++++++-------- > drivers/vfio/mdev/mdev_private.h | 2 + > 2 files changed, 55 insertions(+), 18 deletions(-) > > @@ -265,6 +299,12 @@ int mdev_device_create(struct kobject *kobj, > > mdev->parent = parent; > Adding /* Check if parent unregistration has started */ here as well might be nice, but no need to resend the patch for that. > + if (!down_read_trylock(&parent->unreg_sem)) { > + mdev_device_free(mdev); > + ret = -ENODEV; > + goto mdev_fail; > + } > + > device_initialize(&mdev->dev); > mdev->dev.parent = dev; > mdev->dev.bus = &mdev_bus_type; Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Hi Alex, > -----Original Message----- > From: Cornelia Huck <cohuck@redhat.com> > Sent: Tuesday, June 4, 2019 11:18 AM > To: Parav Pandit <parav@mellanox.com> > Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org; > kwankhede@nvidia.com; alex.williamson@redhat.com; cjia@nvidia.com > Subject: Re: [PATCHv6 3/3] vfio/mdev: Synchronize device create/remove > with parent removal > > On Mon, 3 Jun 2019 13:56:58 -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 accessed > > 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 | 71 ++++++++++++++++++++++++-------- > > drivers/vfio/mdev/mdev_private.h | 2 + > > 2 files changed, 55 insertions(+), 18 deletions(-) > > > > > @@ -265,6 +299,12 @@ int mdev_device_create(struct kobject *kobj, > > > > mdev->parent = parent; > > > > Adding > > /* Check if parent unregistration has started */ > > here as well might be nice, but no need to resend the patch for that. > > > + if (!down_read_trylock(&parent->unreg_sem)) { > > + mdev_device_free(mdev); > > + ret = -ENODEV; > > + goto mdev_fail; > > + } > > + > > device_initialize(&mdev->dev); > > mdev->dev.parent = dev; > > mdev->dev.bus = &mdev_bus_type; > > Reviewed-by: Cornelia Huck <cohuck@redhat.com> Now that we have all 3 patches reviewed and comments addressed, if there are no more comments, can you please take it forward?
On Tue, 11 Jun 2019 03:22:37 +0000 Parav Pandit <parav@mellanox.com> wrote: > Hi Alex, > [snip] > Now that we have all 3 patches reviewed and comments addressed, if > there are no more comments, can you please take it forward? Yep, I put it in a branch rolled into linux-next for upstream testing last week and just sent a pull request to Linus today. Thanks, Alex
> -----Original Message----- > From: Alex Williamson <alex.williamson@redhat.com> > Sent: Tuesday, June 11, 2019 11:25 PM > To: Parav Pandit <parav@mellanox.com> > Cc: Cornelia Huck <cohuck@redhat.com>; kvm@vger.kernel.org; linux- > kernel@vger.kernel.org; kwankhede@nvidia.com; cjia@nvidia.com > Subject: Re: [PATCHv6 3/3] vfio/mdev: Synchronize device create/remove > with parent removal > > On Tue, 11 Jun 2019 03:22:37 +0000 > Parav Pandit <parav@mellanox.com> wrote: > > > Hi Alex, > > > [snip] > > > Now that we have all 3 patches reviewed and comments addressed, if > > there are no more comments, can you please take it forward? > > Yep, I put it in a branch rolled into linux-next for upstream testing last week > and just sent a pull request to Linus today. Thanks, > Oh ok. Great. Thanks Alex.
diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c index 0bef0cae1d4b..c544656191cd 100644 --- a/drivers/vfio/mdev/mdev_core.c +++ b/drivers/vfio/mdev/mdev_core.c @@ -102,11 +102,35 @@ static void mdev_put_parent(struct mdev_parent *parent) kref_put(&parent->ref, mdev_release_parent); } +/* Caller must hold 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; + lockdep_assert_held(&parent->unreg_sem); + 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); + if (dev_is_mdev(dev)) { + struct mdev_device *mdev; + mdev = to_mdev_device(dev); + mdev_device_remove_common(mdev); + } return 0; } @@ -148,6 +172,7 @@ 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; @@ -206,21 +231,23 @@ 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); -static void mdev_device_release(struct device *dev) +static void mdev_device_free(struct mdev_device *mdev) { - struct mdev_device *mdev = to_mdev_device(dev); - mutex_lock(&mdev_list_lock); list_del(&mdev->next); mutex_unlock(&mdev_list_lock); @@ -229,6 +256,13 @@ static void mdev_device_release(struct device *dev) kfree(mdev); } +static void mdev_device_release(struct device *dev) +{ + struct mdev_device *mdev = to_mdev_device(dev); + + mdev_device_free(mdev); +} + int mdev_device_create(struct kobject *kobj, struct device *dev, const guid_t *uuid) { @@ -265,6 +299,12 @@ int mdev_device_create(struct kobject *kobj, mdev->parent = parent; + if (!down_read_trylock(&parent->unreg_sem)) { + mdev_device_free(mdev); + ret = -ENODEV; + goto mdev_fail; + } + device_initialize(&mdev->dev); mdev->dev.parent = dev; mdev->dev.bus = &mdev_bus_type; @@ -287,6 +327,7 @@ 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 +336,7 @@ 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); @@ -305,8 +347,6 @@ 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 +369,13 @@ 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 */ + if (!down_read_trylock(&parent->unreg_sem)) + 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 accessed 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 | 71 ++++++++++++++++++++++++-------- drivers/vfio/mdev/mdev_private.h | 2 + 2 files changed, 55 insertions(+), 18 deletions(-)