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<p>Hey,</p>
<pre>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
</pre>
<div class="moz-cite-prefix">On 2023-03-17 01:22, Matthew Brost
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20230317002221.211065-1-matthew.brost@intel.com">
<pre class="moz-quote-pre" wrap="">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 <a class="moz-txt-link-rfc2396E" href="mailto:matthew.brost@intel.com"><matthew.brost@intel.com></a>
---
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 */
</pre>
</blockquote>
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