tcmu calls uio_unregister_device from tcmu_destroy_device. After that uio will never call tcmu_release for this device. If userspace still had the uio device open and / or mmap'ed during uio_unregister_device, tcmu_release will not be called and udev->kref will never go down to 0.
So tcmu in this situation will not free: - cmds or tmrs still in the queue or the ring - all pages allocated for mailbox and cmd_ring (vmalloc) - all pages allocated for data space - the udev itself The vmalloc'ed area is 8 MB, amount of pages allocated for data space depends on previous usage of the tcmu device. Theoretically that can be up to 1GB. This patch moves the call of uio_unregister_device to the beginning of tcmu_dev_kref_release, which is called when udev->kref drops down to zero. So we know, that uio device is closed and unmap'ed. In case tcmu_realease drops the last kref, we would end up doing the uio_unregister_device from a function called by uio_release, which causes the process to block forever. So we now do the kref_put from new worker function tcmu_release_work_fn which is scheduled by tcmu_release. To make userspace still aware of the device being deleted, tcmu_destroy_device instead of uio_unregister_device now does: - sets a bit in udev, so that tcmu_open and tcmu_mmap can check and fail with -EIO - resets udev->uio_info->irq to 0, so uio will fail read() and write() with -EIO - wakes up userspace possibly waiting in read(), so the read fails with -EIO Avoid possible races in tcmu_open by replacing kref_get with kref_get_unless_zero. Signed-off-by: Bodo Stroesser <[email protected]> --- drivers/target/target_core_user.c | 54 ++++++++++++++++++++++++++++++++++++--- 1 file changed, 50 insertions(+), 4 deletions(-) diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c index 0458bfb143f8..080760985ebf 100644 --- a/drivers/target/target_core_user.c +++ b/drivers/target/target_core_user.c @@ -21,6 +21,7 @@ #include <linux/configfs.h> #include <linux/mutex.h> #include <linux/workqueue.h> +#include <linux/delay.h> #include <net/genetlink.h> #include <scsi/scsi_common.h> #include <scsi/scsi_proto.h> @@ -109,6 +110,7 @@ struct tcmu_nl_cmd { struct tcmu_dev { struct list_head node; struct kref kref; + struct work_struct release_work; struct se_device se_dev; @@ -119,6 +121,7 @@ struct tcmu_dev { #define TCMU_DEV_BIT_BROKEN 1 #define TCMU_DEV_BIT_BLOCKED 2 #define TCMU_DEV_BIT_TMR_NOTIFY 3 +#define TCMU_DEV_BIT_GOING_DOWN 4 unsigned long flags; struct uio_info uio_info; @@ -1527,6 +1530,8 @@ static void tcmu_detach_hba(struct se_hba *hba) hba->hba_ptr = NULL; } +static void tcmu_release_work_fn(struct work_struct *work); + static struct se_device *tcmu_alloc_device(struct se_hba *hba, const char *name) { struct tcmu_dev *udev; @@ -1542,6 +1547,8 @@ static struct se_device *tcmu_alloc_device(struct se_hba *hba, const char *name) return NULL; } + INIT_WORK(&udev->release_work, tcmu_release_work_fn); + udev->hba = hba; udev->cmd_time_out = TCMU_TIME_OUT; udev->qfull_time_out = -1; @@ -1719,6 +1726,9 @@ static int tcmu_mmap(struct uio_info *info, struct vm_area_struct *vma) { struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info); + if (test_bit(TCMU_DEV_BIT_GOING_DOWN, &udev->flags)) + return -EIO; + vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP; vma->vm_ops = &tcmu_vm_ops; @@ -1735,12 +1745,17 @@ static int tcmu_open(struct uio_info *info, struct inode *inode) { struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info); + if (test_bit(TCMU_DEV_BIT_GOING_DOWN, &udev->flags)) + return -EIO; + /* O_EXCL not supported for char devs, so fake it? */ if (test_and_set_bit(TCMU_DEV_BIT_OPEN, &udev->flags)) return -EBUSY; udev->inode = inode; - kref_get(&udev->kref); + if (!kref_get_unless_zero(&udev->kref)) + /* Race between open and device going down */ + return -EIO; pr_debug("open\n"); @@ -1799,6 +1814,8 @@ static void tcmu_dev_kref_release(struct kref *kref) bool all_expired = true; int i; + uio_unregister_device(&udev->uio_info); + vfree(udev->mb_addr); udev->mb_addr = NULL; @@ -1827,6 +1844,15 @@ static void tcmu_dev_kref_release(struct kref *kref) call_rcu(&dev->rcu_head, tcmu_dev_call_rcu); } +static void tcmu_release_work_fn(struct work_struct *work) +{ + struct tcmu_dev *udev = container_of(work, struct tcmu_dev, + release_work); + + /* release ref from open */ + kref_put(&udev->kref, tcmu_dev_kref_release); +} + static int tcmu_release(struct uio_info *info, struct inode *inode) { struct tcmu_dev *udev = container_of(info, struct tcmu_dev, uio_info); @@ -1834,8 +1860,17 @@ static int tcmu_release(struct uio_info *info, struct inode *inode) clear_bit(TCMU_DEV_BIT_OPEN, &udev->flags); pr_debug("close\n"); - /* release ref from open */ - kref_put(&udev->kref, tcmu_dev_kref_release); + + /* + * We must not put kref directly from here, since dropping down kref to + * zero would implicitly call tcmu_dev_kref_release, which calls + * uio_unregister_device --> process hangs forever, since tcmu_release + * is called from uio. + * So we leave it to tcmu_release_work_fn to put the kref. + */ + while (!schedule_work(&udev->release_work)) + usleep_range(1000, 5000); + return 0; } @@ -2166,7 +2201,18 @@ static void tcmu_destroy_device(struct se_device *dev) tcmu_send_dev_remove_event(udev); - uio_unregister_device(&udev->uio_info); + /* + * We must not call uio_unregister_device here. If there is a userspace + * process with open or mmap'ed uio device, uio would not call + * tcmu_release on later unmap or close. + */ + + /* reset uio_info->irq, so uio will reject read() and write() */ + udev->uio_info.irq = 0; + /* Set bit, so we can reject later calls to tcmu_open and tcmu_mmap */ + set_bit(TCMU_DEV_BIT_GOING_DOWN, &udev->flags); + /* wake up possible sleeper in uio_read(), it will return -EIO */ + uio_event_notify(&udev->uio_info); /* release ref from configure */ kref_put(&udev->kref, tcmu_dev_kref_release); -- 2.12.3
