Re: [PATCH 1/1 repost #1] DRM: don't enable irqs in locking

[Dave Airlie]

On Fri, Jul 25, 2008 at 6:42 PM, Jiri Slaby <jirislaby@xxxxxxxxx> wrote:
> drm_lock_take(); and drm_lock_free(); are called from
> drm_locked_tasklet_func(); which disables interrupts when grabbing its
> spinlock.
>
> Don't allow these locking functions to re-enable interrupts when
> the tasklet expects them disabled. I.e. use spin_lock_irqsave instead of
> spin_lock_bh (with their unlock opposites).

Hmm this has bounced through 2-3 variations.. Thomas any ideas what
the final correct answer is?

Dave.

>
> We will get such a warnings otherwise:
> ------------[ cut here ]------------
> WARNING: at kernel/softirq.c:136 local_bh_enable_ip+0x8b/0xb0()
> Modules linked in: arc4 ecb crypto_blkcipher cryptomgr crypto_algapi ath5k usbhid mac80211 ohci1394 hid led_class floppy cfg80211 ff_memless ieee1394 rtc_cmos evdev [last unloaded: freq_table]
> Pid: 0, comm: swapper Not tainted 2.6.26-rc8-mm1_64 #427
>
> Call Trace:
>  <IRQ>  [<ffffffff8023813f>] warn_on_slowpath+0x5f/0x90
> [...]
>  [<ffffffff8023e1fb>] local_bh_enable_ip+0x8b/0xb0
>  [<ffffffff8055b2cf>] _spin_unlock_bh+0xf/0x20
>  [<ffffffff803b0bd1>] drm_lock_take+0x81/0xe0
>  [<ffffffff803b006b>] drm_locked_tasklet_func+0x4b/0xb0
>  [<ffffffff8023daf9>] tasklet_hi_action+0x69/0xf0
>  [<ffffffff8023e3e4>] __do_softirq+0x84/0xf0
> [stack snipped]
>
> Signed-off-by: Jiri Slaby <jirislaby@xxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxx>
> ---
>  drivers/gpu/drm/drm_lock.c |   12 +++++++-----
>  1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_lock.c b/drivers/gpu/drm/drm_lock.c
> index 0998723..79943e4 100644
> --- a/drivers/gpu/drm/drm_lock.c
> +++ b/drivers/gpu/drm/drm_lock.c
> @@ -196,10 +196,11 @@ int drm_unlock(struct drm_device *dev, void *data, struct drm_file *file_priv)
>  int drm_lock_take(struct drm_lock_data *lock_data,
>                  unsigned int context)
>  {
> +       unsigned long flags;
>        unsigned int old, new, prev;
>        volatile unsigned int *lock = &lock_data->hw_lock->lock;
>
> -       spin_lock_bh(&lock_data->spinlock);
> +       spin_lock_irqsave(&lock_data->spinlock, flags);
>        do {
>                old = *lock;
>                if (old & _DRM_LOCK_HELD)
> @@ -211,7 +212,7 @@ int drm_lock_take(struct drm_lock_data *lock_data,
>                }
>                prev = cmpxchg(lock, old, new);
>        } while (prev != old);
> -       spin_unlock_bh(&lock_data->spinlock);
> +       spin_unlock_irqrestore(&lock_data->spinlock, flags);
>
>        if (_DRM_LOCKING_CONTEXT(old) == context) {
>                if (old & _DRM_LOCK_HELD) {
> @@ -270,17 +271,18 @@ static int drm_lock_transfer(struct drm_lock_data *lock_data,
>  */
>  int drm_lock_free(struct drm_lock_data *lock_data, unsigned int context)
>  {
> +       unsigned long flags;
>        unsigned int old, new, prev;
>        volatile unsigned int *lock = &lock_data->hw_lock->lock;
>
> -       spin_lock_bh(&lock_data->spinlock);
> +       spin_lock_irqsave(&lock_data->spinlock, flags);
>        if (lock_data->kernel_waiters != 0) {
>                drm_lock_transfer(lock_data, 0);
>                lock_data->idle_has_lock = 1;
> -               spin_unlock_bh(&lock_data->spinlock);
> +               spin_unlock_irqrestore(&lock_data->spinlock, flags);
>                return 1;
>        }
> -       spin_unlock_bh(&lock_data->spinlock);
> +       spin_unlock_irqrestore(&lock_data->spinlock, flags);
>
>        do {
>                old = *lock;
> --
> 1.5.6.2
>
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