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SubjectRe: [PATCH 1/1 repost #1] DRM: don't enable irqs in locking
Dave Airlie wrote:
> On Fri, Jul 25, 2008 at 6:42 PM, Jiri Slaby <jirislaby@gmail.com> 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.
>
Hmm,
Yes, this bug could occur, but the remedy is not to use
spin_lock_irqsave() for lock_data::spinlock but to avoid calling
drm_lock_take with the drm_device::tasklet_lock held with irqs disabled.
I'll see if I can come up with a patch.

/Thomas


>> 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@gmail.com>
>> Cc: David Airlie <airlied@linux.ie>
>> ---
>> 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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>>





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