Messages in this thread | | | Date | Mon, 28 Jul 2008 22:32:45 +0200 | From | Thomas Hellström <> | Subject | Re: [PATCH 1/1 repost #1] DRM: don't enable irqs in locking |
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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 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> >>
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