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    Subject[PATCH 4.19 069/118] vfio: Fix WARNING "do not call blocking ops when !TASK_RUNNING"
    Date
    [ Upstream commit 41be3e2618174fdf3361e49e64f2bf530f40c6b0 ]

    vfio_dev_present() which is the condition to
    wait_event_interruptible_timeout(), will call vfio_group_get_device
    and try to acquire the mutex group->device_lock.

    wait_event_interruptible_timeout() will set the state of the current
    task to TASK_INTERRUPTIBLE, before doing the condition check. This
    means that we will try to acquire the mutex while already in a
    sleeping state. The scheduler warns us by giving the following
    warning:

    [ 4050.264464] ------------[ cut here ]------------
    [ 4050.264508] do not call blocking ops when !TASK_RUNNING; state=1 set at [<00000000b33c00e2>] prepare_to_wait_event+0x14a/0x188
    [ 4050.264529] WARNING: CPU: 12 PID: 35924 at kernel/sched/core.c:6112 __might_sleep+0x76/0x90
    ....

    4050.264756] Call Trace:
    [ 4050.264765] ([<000000000017bbaa>] __might_sleep+0x72/0x90)
    [ 4050.264774] [<0000000000b97edc>] __mutex_lock+0x44/0x8c0
    [ 4050.264782] [<0000000000b9878a>] mutex_lock_nested+0x32/0x40
    [ 4050.264793] [<000003ff800d7abe>] vfio_group_get_device+0x36/0xa8 [vfio]
    [ 4050.264803] [<000003ff800d87c0>] vfio_del_group_dev+0x238/0x378 [vfio]
    [ 4050.264813] [<000003ff8015f67c>] mdev_remove+0x3c/0x68 [mdev]
    [ 4050.264825] [<00000000008e01b0>] device_release_driver_internal+0x168/0x268
    [ 4050.264834] [<00000000008de692>] bus_remove_device+0x162/0x190
    [ 4050.264843] [<00000000008daf42>] device_del+0x1e2/0x368
    [ 4050.264851] [<00000000008db12c>] device_unregister+0x64/0x88
    [ 4050.264862] [<000003ff8015ed84>] mdev_device_remove+0xec/0x130 [mdev]
    [ 4050.264872] [<000003ff8015f074>] remove_store+0x6c/0xa8 [mdev]
    [ 4050.264881] [<000000000046f494>] kernfs_fop_write+0x14c/0x1f8
    [ 4050.264890] [<00000000003c1530>] __vfs_write+0x38/0x1a8
    [ 4050.264899] [<00000000003c187c>] vfs_write+0xb4/0x198
    [ 4050.264908] [<00000000003c1af2>] ksys_write+0x5a/0xb0
    [ 4050.264916] [<0000000000b9e270>] system_call+0xdc/0x2d8
    [ 4050.264925] 4 locks held by sh/35924:
    [ 4050.264933] #0: 000000001ef90325 (sb_writers#4){.+.+}, at: vfs_write+0x9e/0x198
    [ 4050.264948] #1: 000000005c1ab0b3 (&of->mutex){+.+.}, at: kernfs_fop_write+0x1cc/0x1f8
    [ 4050.264963] #2: 0000000034831ab8 (kn->count#297){++++}, at: kernfs_remove_self+0x12e/0x150
    [ 4050.264979] #3: 00000000e152484f (&dev->mutex){....}, at: device_release_driver_internal+0x5c/0x268
    [ 4050.264993] Last Breaking-Event-Address:
    [ 4050.265002] [<000000000017bbaa>] __might_sleep+0x72/0x90
    [ 4050.265010] irq event stamp: 7039
    [ 4050.265020] hardirqs last enabled at (7047): [<00000000001cee7a>] console_unlock+0x6d2/0x740
    [ 4050.265029] hardirqs last disabled at (7054): [<00000000001ce87e>] console_unlock+0xd6/0x740
    [ 4050.265040] softirqs last enabled at (6416): [<0000000000b8fe26>] __udelay+0xb6/0x100
    [ 4050.265049] softirqs last disabled at (6415): [<0000000000b8fe06>] __udelay+0x96/0x100
    [ 4050.265057] ---[ end trace d04a07d39d99a9f9 ]---

    Let's fix this as described in the article
    https://lwn.net/Articles/628628/.

    Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
    [remove now redundant vfio_dev_present()]
    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/vfio/vfio.c | 30 ++++++++++--------------------
    1 file changed, 10 insertions(+), 20 deletions(-)

    diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
    index 64833879f75d..7a386fb30bf1 100644
    --- a/drivers/vfio/vfio.c
    +++ b/drivers/vfio/vfio.c
    @@ -34,6 +34,7 @@
    #include <linux/uaccess.h>
    #include <linux/vfio.h>
    #include <linux/wait.h>
    +#include <linux/sched/signal.h>

    #define DRIVER_VERSION "0.3"
    #define DRIVER_AUTHOR "Alex Williamson <alex.williamson@redhat.com>"
    @@ -904,30 +905,17 @@ void *vfio_device_data(struct vfio_device *device)
    }
    EXPORT_SYMBOL_GPL(vfio_device_data);

    -/* Given a referenced group, check if it contains the device */
    -static bool vfio_dev_present(struct vfio_group *group, struct device *dev)
    -{
    - struct vfio_device *device;
    -
    - device = vfio_group_get_device(group, dev);
    - if (!device)
    - return false;
    -
    - vfio_device_put(device);
    - return true;
    -}
    -
    /*
    * Decrement the device reference count and wait for the device to be
    * removed. Open file descriptors for the device... */
    void *vfio_del_group_dev(struct device *dev)
    {
    + DEFINE_WAIT_FUNC(wait, woken_wake_function);
    struct vfio_device *device = dev_get_drvdata(dev);
    struct vfio_group *group = device->group;
    void *device_data = device->device_data;
    struct vfio_unbound_dev *unbound;
    unsigned int i = 0;
    - long ret;
    bool interrupted = false;

    /*
    @@ -964,6 +952,8 @@ void *vfio_del_group_dev(struct device *dev)
    * interval with counter to allow the driver to take escalating
    * measures to release the device if it has the ability to do so.
    */
    + add_wait_queue(&vfio.release_q, &wait);
    +
    do {
    device = vfio_group_get_device(group, dev);
    if (!device)
    @@ -975,12 +965,10 @@ void *vfio_del_group_dev(struct device *dev)
    vfio_device_put(device);

    if (interrupted) {
    - ret = wait_event_timeout(vfio.release_q,
    - !vfio_dev_present(group, dev), HZ * 10);
    + wait_woken(&wait, TASK_UNINTERRUPTIBLE, HZ * 10);
    } else {
    - ret = wait_event_interruptible_timeout(vfio.release_q,
    - !vfio_dev_present(group, dev), HZ * 10);
    - if (ret == -ERESTARTSYS) {
    + wait_woken(&wait, TASK_INTERRUPTIBLE, HZ * 10);
    + if (signal_pending(current)) {
    interrupted = true;
    dev_warn(dev,
    "Device is currently in use, task"
    @@ -989,8 +977,10 @@ void *vfio_del_group_dev(struct device *dev)
    current->comm, task_pid_nr(current));
    }
    }
    - } while (ret <= 0);

    + } while (1);
    +
    + remove_wait_queue(&vfio.release_q, &wait);
    /*
    * In order to support multiple devices per group, devices can be
    * plucked from the group while other devices in the group are still
    --
    2.20.1


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