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SubjectRe: i915 X lockup
On Fri, 27 Feb 2009 10:28:51 +0100 Jiri Slaby <jirislaby@gmail.com> wrote:

> everytime I run X, it gets stuck. Currently running on mmotm
> 2009-02-26-16-58, but I think this is wider problem. I had i915 disabled
> for a long time (until I noticed today).
>
> SysRq : Show Locks Held
>
> Showing all locks held in the system:
> 3 locks held by events/0/10:
> #0: (events){+.+.+.}, at: [<ffffffff8025223d>] worker_thread+0x19d/0x340
> #1: (&(&dev_priv->mm.retire_work)->work){+.+...}, at:
> [<ffffffff8025223d>] worker_thread+0x19d/0x340
> #2: (&dev->struct_mutex){+.+.+.}, at: [<ffffffff804057ba>]
> i915_gem_retire_work_handler+0x3a/0x90
> 1 lock held by mingetty/3899:
> #0: (&tty->atomic_read_lock){+.+.+.}, at: [<ffffffff803cb5de>]
> n_tty_read+0x48e/0x8e0
> 1 lock held by mingetty/3900:
> #0: (&tty->atomic_read_lock){+.+.+.}, at: [<ffffffff803cb5de>]
> n_tty_read+0x48e/0x8e0
> 1 lock held by mingetty/3901:
> #0: (&tty->atomic_read_lock){+.+.+.}, at: [<ffffffff803cb5de>]
> n_tty_read+0x48e/0x8e0
> 1 lock held by X/4007:
> #0: (&dev->struct_mutex){+.+.+.}, at: [<ffffffff8040563c>]
> i915_gem_throttle_ioctl+0x2c/0x60
> 2 locks held by bash/4105:
> #0: (sysrq_key_table_lock){......}, at: [<ffffffff803de366>]
> __handle_sysrq+0x26/0x190
> #1: (tasklist_lock){.+.+..}, at: [<ffffffff80266c1f>]
> debug_show_all_locks+0x3f/0x1c0

I assume that i915_gem_throttle_ioctl->i915_gem_ring_throttle is stuck
in i915_wait_request(), holding struct_mutex. That of course makes
keventd block.

Perhaps i915_wait_request() is waiting for keventd to do something,
which is the deadlock. That "something" could be to simply finish its
current call to i915_gem_retire_work_handler().

But worse, it could be some completely other keventd handler which
isn't getting run, because that keventd instance is stuck over in
i915_gem_retire_work_handler().

IOW, the usual keventd problem.


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