[Intel-xe] [PATCH] drm/xe: Fix locking in CT fast path
Maarten Lankhorst
maarten.lankhorst at linux.intel.com
Tue Mar 21 12:25:51 UTC 2023
Hey,
I'm afraid this is not allowed, you can't take a mutex in an irq handler, not even a trylock.
From Documentation/locking/mutex-design.rst:
The mutex subsystem checks and enforces the following rules:
...
- Mutexes may not be used in hardware or software interrupt
contexts such as tasklets and timers.
Lockdep will likely still splat too as a result.
Cheers,
~Maarten
On 2023-03-17 01:22, Matthew Brost wrote:
> We can't sleep in the CT fast but need to ensure we can access VRAM. Use
> a trylock + reference counter check to ensure safe access to VRAM, if
> either check fails, fall back to slow path.
>
> VLK-45296
>
> Signed-off-by: Matthew Brost<matthew.brost at intel.com>
> ---
> drivers/gpu/drm/xe/xe_device.h | 9 ++++++++-
> drivers/gpu/drm/xe/xe_guc_ct.c | 11 ++++++++++-
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
> index 25c5087f5aad..0cc4f52098a1 100644
> --- a/drivers/gpu/drm/xe/xe_device.h
> +++ b/drivers/gpu/drm/xe/xe_device.h
> @@ -95,12 +95,19 @@ static inline void xe_device_assert_mem_access(struct xe_device *xe)
> XE_WARN_ON(!xe->mem_access.ref);
> }
>
> +static inline bool __xe_device_mem_access_ongoing(struct xe_device *xe)
> +{
> + lockdep_assert_held(&xe->mem_access.lock);
> +
> + return xe->mem_access.ref;
> +}
> +
> static inline bool xe_device_mem_access_ongoing(struct xe_device *xe)
> {
> bool ret;
>
> mutex_lock(&xe->mem_access.lock);
> - ret = xe->mem_access.ref;
> + ret = __xe_device_mem_access_ongoing(xe);
> mutex_unlock(&xe->mem_access.lock);
>
> return ret;
> diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
> index e5ed9022a0a2..bba0ef21c9e5 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ct.c
> +++ b/drivers/gpu/drm/xe/xe_guc_ct.c
> @@ -1030,9 +1030,15 @@ void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
> struct xe_device *xe = ct_to_xe(ct);
> int len;
>
> - if (!xe_device_in_fault_mode(xe) || !xe_device_mem_access_ongoing(xe))
> + if (!xe_device_in_fault_mode(xe))
> return;
>
> + if (!mutex_trylock(&xe->mem_access.lock))
> + return;
> +
> + if (!__xe_device_mem_access_ongoing(xe))
> + goto unlock;
> +
> spin_lock(&ct->fast_lock);
> do {
> len = g2h_read(ct, ct->fast_msg, true);
> @@ -1040,6 +1046,9 @@ void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
> g2h_fast_path(ct, ct->fast_msg, len);
> } while (len > 0);
> spin_unlock(&ct->fast_lock);
> +
> +unlock:
> + mutex_unlock(&xe->mem_access.lock);
> }
>
> /* Returns less than zero on error, 0 on done, 1 on more available */
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