[Intel-xe] [PATCH v7 6/7] drm/xe: fix xe_device_mem_access_get() races
Matthew Auld
matthew.auld at intel.com
Mon May 22 16:14:02 UTC 2023
It looks like there is at least one race here, given that the
pm_runtime_suspended() check looks to return false if we are in the
process of suspending the device (RPM_SUSPENDING vs RPM_SUSPENDED). We
later also do xe_pm_runtime_get_if_active(), but since the device is
suspending or has now suspended, this doesn't do anything either.
Following from this we can potentially return from
xe_device_mem_access_get() with the device suspended or about to be,
leading to broken behaviour.
Attempt to fix this by always grabbing the runtime ref when our
internal ref transitions from 0 -> 1, and then wrap the whole thing with
a lock to ensure callers are serialized.
v2:
- ct->lock looks to be primed with fs_reclaim, so holding that and then
allocating memory will cause lockdep to complain. Now that we
unconditionally grab the mem_access.lock around mem_access_{get,put}, we
need to change the ordering wrt to grabbing the ct->lock, since some of
the runtime_pm routines can allocate memory (or at least that's what
lockdep seems to suggest). Hopefully not a big deal. It might be that
there were already issues with this, just that the atomics where
"hiding" the potential issues.
v3:
- Use Thomas Hellström' idea with tracking the active task that is
executing in the resume or suspend callback, in order to avoid
recursive resume/suspend calls deadlocking on itself.
- Split the ct->lock change.
v4:
- Add smb_mb() around accessing the pm_callback_task for extra safety.
(Thomas Hellström)
v5:
- Clarify the kernel-doc for the mem_access.lock, given that it is quite
strange in what it protects (data vs code). The real motivation is to
aid lockdep. (Rodrigo Vivi)
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/258
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
drivers/gpu/drm/xe/xe_device.c | 52 +++++++++++++++++++---
drivers/gpu/drm/xe/xe_device.h | 17 +------
drivers/gpu/drm/xe/xe_device_types.h | 19 +++++++-
drivers/gpu/drm/xe/xe_pm.c | 66 +++++++++++++++++++---------
drivers/gpu/drm/xe/xe_pm.h | 3 +-
5 files changed, 112 insertions(+), 45 deletions(-)
diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index d0297ee432b2..55f974b1ee78 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -403,24 +403,62 @@ u32 xe_device_ccs_bytes(struct xe_device *xe, u64 size)
DIV_ROUND_UP(size, NUM_BYTES_PER_CCS_BYTE) : 0;
}
+void xe_device_assert_mem_access(struct xe_device *xe)
+{
+ if (xe_pm_read_callback_task(xe) == current)
+ return;
+
+ XE_WARN_ON(!xe->mem_access.ref);
+}
+
+bool xe_device_mem_access_ongoing(struct xe_device *xe)
+{
+ bool ret;
+
+ if (xe_pm_read_callback_task(xe) == current)
+ return true;
+
+ mutex_lock(&xe->mem_access.lock);
+ ret = xe->mem_access.ref;
+ mutex_unlock(&xe->mem_access.lock);
+
+ return ret;
+}
+
void xe_device_mem_access_get(struct xe_device *xe)
{
- bool resumed = xe_pm_runtime_resume_if_suspended(xe);
+ /*
+ * This looks racy, but should be fine since the pm_callback_task only
+ * transitions from NULL -> current (and back to NULL again), during the
+ * runtime_resume() or runtime_suspend() callbacks, for which there can
+ * only be a single one running for our device. We only need to prevent
+ * recursively calling the runtime_get or runtime_put from those
+ * callbacks, as well as preventing triggering any access_ongoing
+ * asserts.
+ */
+ if (xe_pm_read_callback_task(xe) == current)
+ return;
+ /*
+ * It's possible to get rid of the mem_access.lock here, however lockdep
+ * has an easier time digesting the mem_access.lock -> runtime_pm chain
+ * (and any locks the caller is holding), on all transitions, and not
+ * for example just on the 0 -> 1.
+ */
mutex_lock(&xe->mem_access.lock);
- if (xe->mem_access.ref++ == 0)
- xe->mem_access.hold_rpm = xe_pm_runtime_get_if_active(xe);
+ if (xe->mem_access.ref == 0)
+ xe->mem_access.hold_rpm = xe_pm_runtime_resume_and_get(xe);
+ xe->mem_access.ref++;
mutex_unlock(&xe->mem_access.lock);
- /* The usage counter increased if device was immediately resumed */
- if (resumed)
- xe_pm_runtime_put(xe);
-
XE_WARN_ON(xe->mem_access.ref == S32_MAX);
}
void xe_device_mem_access_put(struct xe_device *xe)
{
+ if (xe_pm_read_callback_task(xe) == current)
+ return;
+
mutex_lock(&xe->mem_access.lock);
if (--xe->mem_access.ref == 0 && xe->mem_access.hold_rpm)
xe_pm_runtime_put(xe);
diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
index 9ab7e6134f89..64576ed9323e 100644
--- a/drivers/gpu/drm/xe/xe_device.h
+++ b/drivers/gpu/drm/xe/xe_device.h
@@ -90,21 +90,8 @@ static inline struct xe_force_wake * gt_to_fw(struct xe_gt *gt)
void xe_device_mem_access_get(struct xe_device *xe);
void xe_device_mem_access_put(struct xe_device *xe);
-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)
-{
- bool ret;
-
- mutex_lock(&xe->mem_access.lock);
- ret = xe->mem_access.ref;
- mutex_unlock(&xe->mem_access.lock);
-
- return ret;
-}
+void xe_device_assert_mem_access(struct xe_device *xe);
+bool xe_device_mem_access_ongoing(struct xe_device *xe);
static inline bool xe_device_in_fault_mode(struct xe_device *xe)
{
diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index 4d1af6663ab1..b5a56e112c0a 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -260,7 +260,18 @@ struct xe_device {
* triggering additional actions when they occur.
*/
struct {
- /** @lock: protect the ref count */
+ /**
+ * @lock: Protects @ref and serializes multiple callers.
+ *
+ * Also used as lockdep aid to hopefully ensure that it sees
+ * that the runtime_pm callbacks can be called while holding
+ * @lock, and therefore any locks that the caller is holding
+ * also have a clear dependency on the @lock and any locks the
+ * runtime_pm callbacks grab, since there will be a dependency
+ * for all @ref transitions (since we always grab the @lock) and
+ * not just for 0 -> 1, if we have a chain like: (callers_locks)
+ * -> access.lock -> runtime_pm callbacks.
+ */
struct mutex lock;
/** @ref: ref count of memory accesses */
s32 ref;
@@ -268,6 +279,12 @@ struct xe_device {
bool hold_rpm;
} mem_access;
+ /**
+ * @pm_callback_task: Track the active task that is running in either
+ * the runtime_suspend or runtime_resume callbacks.
+ */
+ struct task_struct *pm_callback_task;
+
/** @d3cold_allowed: Indicates if d3cold is a valid device state */
bool d3cold_allowed;
diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
index b7b57f10ba25..29c8861e58a5 100644
--- a/drivers/gpu/drm/xe/xe_pm.c
+++ b/drivers/gpu/drm/xe/xe_pm.c
@@ -137,43 +137,71 @@ void xe_pm_runtime_fini(struct xe_device *xe)
pm_runtime_forbid(dev);
}
+static void xe_pm_write_callback_task(struct xe_device *xe,
+ struct task_struct *task)
+{
+ WRITE_ONCE(xe->pm_callback_task, task);
+
+ /*
+ * Just in case it's somehow possible for our writes to be reordered to
+ * the extent that something else re-uses the task written in
+ * pm_callback_task. For example after returning from the callback, but
+ * before the reordered write that resets pm_callback_task back to NULL.
+ */
+ smp_mb(); /* pairs with xe_pm_read_callback_task */
+}
+
+struct task_struct *xe_pm_read_callback_task(struct xe_device *xe)
+{
+ smp_mb(); /* pairs with xe_pm_write_callback_task */
+
+ return READ_ONCE(xe->pm_callback_task);
+}
+
int xe_pm_runtime_suspend(struct xe_device *xe)
{
struct xe_gt *gt;
u8 id;
- int err;
+ int err = 0;
+
+ if (xe->d3cold_allowed && xe_device_mem_access_ongoing(xe))
+ return -EBUSY;
+
+ /* Disable access_ongoing asserts and prevent recursive pm calls */
+ xe_pm_write_callback_task(xe, current);
if (xe->d3cold_allowed) {
- if (xe_device_mem_access_ongoing(xe))
- return -EBUSY;
-
err = xe_bo_evict_all(xe);
if (err)
- return err;
+ goto out;
}
for_each_gt(gt, xe, id) {
err = xe_gt_suspend(gt);
if (err)
- return err;
+ goto out;
}
xe_irq_suspend(xe);
-
- return 0;
+out:
+ xe_pm_write_callback_task(xe, NULL);
+ return err;
}
int xe_pm_runtime_resume(struct xe_device *xe)
{
struct xe_gt *gt;
u8 id;
- int err;
+ int err = 0;
+
+ /* Disable access_ongoing asserts and prevent recursive pm calls */
+ xe_pm_write_callback_task(xe, current);
if (xe->d3cold_allowed) {
for_each_gt(gt, xe, id) {
err = xe_pcode_init(gt);
if (err)
- return err;
+ goto out;
}
/*
@@ -182,7 +210,7 @@ int xe_pm_runtime_resume(struct xe_device *xe)
*/
err = xe_bo_restore_kernel(xe);
if (err)
- return err;
+ goto out;
}
xe_irq_resume(xe);
@@ -193,10 +221,11 @@ int xe_pm_runtime_resume(struct xe_device *xe)
if (xe->d3cold_allowed) {
err = xe_bo_restore_user(xe);
if (err)
- return err;
+ goto out;
}
-
- return 0;
+out:
+ xe_pm_write_callback_task(xe, NULL);
+ return err;
}
int xe_pm_runtime_get(struct xe_device *xe)
@@ -210,14 +239,9 @@ int xe_pm_runtime_put(struct xe_device *xe)
return pm_runtime_put_autosuspend(xe->drm.dev);
}
-/* Return true if resume operation happened and usage count was increased */
-bool xe_pm_runtime_resume_if_suspended(struct xe_device *xe)
+bool xe_pm_runtime_resume_and_get(struct xe_device *xe)
{
- /* In case we are suspended we need to immediately wake up */
- if (pm_runtime_suspended(xe->drm.dev))
- return !pm_runtime_resume_and_get(xe->drm.dev);
-
- return false;
+ return !pm_runtime_resume_and_get(xe->drm.dev);
}
int xe_pm_runtime_get_if_active(struct xe_device *xe)
diff --git a/drivers/gpu/drm/xe/xe_pm.h b/drivers/gpu/drm/xe/xe_pm.h
index 6a885585f653..e92c508d44b9 100644
--- a/drivers/gpu/drm/xe/xe_pm.h
+++ b/drivers/gpu/drm/xe/xe_pm.h
@@ -19,7 +19,8 @@ int xe_pm_runtime_suspend(struct xe_device *xe);
int xe_pm_runtime_resume(struct xe_device *xe);
int xe_pm_runtime_get(struct xe_device *xe);
int xe_pm_runtime_put(struct xe_device *xe);
-bool xe_pm_runtime_resume_if_suspended(struct xe_device *xe);
+bool xe_pm_runtime_resume_and_get(struct xe_device *xe);
int xe_pm_runtime_get_if_active(struct xe_device *xe);
+struct task_struct *xe_pm_read_callback_task(struct xe_device *xe);
#endif
--
2.40.1
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