Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> If we hit an error while allocating the page tables, we have to unwind
> the incomplete updates, and wish to free the unused pd. However, we are
> not allowed to be hoding the spinlock at that point, and so must use the
> later free to defer it until after we drop the lock.
>
> <3> [414.363795] BUG: sleeping function called from invalid context at drivers/gpu/drm/i915/i915_gem_gtt.c:472
> <3> [414.364167] in_atomic(): 1, irqs_disabled(): 0, pid: 3905, name: i915_selftest
> <4> [414.364406] 3 locks held by i915_selftest/3905:
> <4> [414.364408] #0: 0000000034fe8aa8 (&dev->mutex){....}, at: device_driver_attach+0x18/0x50
> <4> [414.364415] #1: 000000006bd8a560 (&dev->struct_mutex){+.+.}, at: igt_ctx_exec+0xb7/0x410 [i915]
> <4> [414.364476] #2: 000000003dfdc766 (&(&pd->lock)->rlock){+.+.}, at: gen8_ppgtt_alloc_pdp+0x448/0x540 [i915]
> <3> [414.364529] Preemption disabled at:
> <4> [414.364530] [<0000000000000000>] 0x0
> <4> [414.364696] CPU: 0 PID: 3905 Comm: i915_selftest Tainted: G U 5.2.0-rc7-CI-CI_DRM_6403+ #1
> <4> [414.364698] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.1-0-g8891697-prebuilt.qemu-project.org 04/01/2014
> <4> [414.364699] Call Trace:
> <4> [414.364704] dump_stack+0x67/0x9b
> <4> [414.364708] ___might_sleep+0x167/0x250
> <4> [414.364777] vm_free_page+0x24/0xc0 [i915]
> <4> [414.364852] free_pd+0xf/0x20 [i915]
> <4> [414.364897] gen8_ppgtt_alloc_pdp+0x489/0x540 [i915]
> <4> [414.364946] gen8_ppgtt_alloc_4lvl+0x8e/0x2e0 [i915]
> <4> [414.364992] ppgtt_bind_vma+0x2e/0x60 [i915]
> <4> [414.365039] i915_vma_bind+0xe8/0x2c0 [i915]
> <4> [414.365088] __i915_vma_do_pin+0xa1/0xd20 [i915]
>
> Fixes: 1d1b5490b91c ("drm/i915/gtt: Replace struct_mutex serialisation for allocation")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
>From another thread,
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_gtt.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 9e76347e039e..1065753e86fb 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -1489,7 +1489,8 @@ static int gen8_ppgtt_alloc_pdp(struct i915_address_space *vm,
> gen8_ppgtt_set_pdpe(pdp, vm->scratch_pd, pdpe);
> GEM_BUG_ON(!atomic_read(&pdp->used));
> atomic_dec(&pdp->used);
> - free_pd(vm, pd);
> + GEM_BUG_ON(alloc);
> + alloc = pd; /* defer the free to after the lock */
> }
> spin_unlock(&pdp->lock);
> unwind:
> @@ -1558,7 +1559,8 @@ static int gen8_ppgtt_alloc_4lvl(struct i915_address_space *vm,
> spin_lock(&pml4->lock);
> if (atomic_dec_and_test(&pdp->used)) {
> gen8_ppgtt_set_pml4e(pml4, vm->scratch_pdp, pml4e);
> - free_pd(vm, pdp);
> + GEM_BUG_ON(alloc);
> + alloc = pdp; /* defer the free until after the lock */
> }
> spin_unlock(&pml4->lock);
> unwind:
> --
> 2.20.1
>
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