[Intel-xe] [PATCH v14 01/10] drm/xe: fix xe_device_mem_access_get() races
Matthew Auld
matthew.auld at intel.com
Mon Jul 17 11:25:04 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. The hard part is then dealing with the
runtime_pm callbacks also calling xe_device_mem_access_get() and
deadlocking, which the pm_runtime_suspended() check prevented.
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)
v6:
- Split out the lock change. We still want this as a lockdep aid but
only for the xe_device_mem_access_get() path. Sticking a lock on the
put() looks be a no-go, also the runtime_put() there is always async.
- Now that the lock is gone move to atomics and rely on the pm code
serialising multiple callers on the 0 -> 1 transition.
- g2h_worker_func() looks to be the next issue, given that
suspend-resume callbacks are using CT, so try to handle that.
v7:
- Add xe_device_mem_access_get_if_ongoing(), and use it in
g2h_worker_func().
v8 (Anshuman):
- Just always grab the rpm, instead of just on the 0 -> 1 transition,
which is a lot clearer and simplifies the code quite a bit.
v9:
- Make sure we also adjust the CT fast-path with if-active.
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>
Cc: Anshuman Gupta <anshuman.gupta at intel.com>
Acked-by: Anshuman Gupta <anshuman.gupta at intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
drivers/gpu/drm/xe/xe_device.c | 58 +++++++++++++++++++-----
drivers/gpu/drm/xe/xe_device.h | 11 +----
drivers/gpu/drm/xe/xe_device_types.h | 8 +++-
drivers/gpu/drm/xe/xe_guc_ct.c | 41 +++++++++++++++--
drivers/gpu/drm/xe/xe_pm.c | 68 ++++++++++++++++++----------
drivers/gpu/drm/xe/xe_pm.h | 2 +-
6 files changed, 135 insertions(+), 53 deletions(-)
diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
index 42fedb267454..ba2b83925ded 100644
--- a/drivers/gpu/drm/xe/xe_device.c
+++ b/drivers/gpu/drm/xe/xe_device.c
@@ -412,33 +412,67 @@ u32 xe_device_ccs_bytes(struct xe_device *xe, u64 size)
DIV_ROUND_UP(size, NUM_BYTES_PER_CCS_BYTE) : 0;
}
+bool xe_device_mem_access_ongoing(struct xe_device *xe)
+{
+ if (xe_pm_read_callback_task(xe) != NULL)
+ return true;
+
+ return atomic_read(&xe->mem_access.ref);
+}
+
+void xe_device_assert_mem_access(struct xe_device *xe)
+{
+ XE_WARN_ON(!xe_device_mem_access_ongoing(xe));
+}
+
bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe)
{
- return atomic_inc_not_zero(&xe->mem_access.ref);
+ bool active;
+
+ if (xe_pm_read_callback_task(xe) == current)
+ return true;
+
+ active = xe_pm_runtime_get_if_active(xe);
+ if (active) {
+ int ref = atomic_inc_return(&xe->mem_access.ref);
+
+ XE_WARN_ON(ref == S32_MAX);
+ }
+
+ return active;
}
void xe_device_mem_access_get(struct xe_device *xe)
{
- bool resumed = xe_pm_runtime_resume_if_suspended(xe);
- int ref = atomic_inc_return(&xe->mem_access.ref);
+ int ref;
- if (ref == 1)
- xe->mem_access.hold_rpm = xe_pm_runtime_get_if_active(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;
- /* The usage counter increased if device was immediately resumed */
- if (resumed)
- xe_pm_runtime_put(xe);
+ xe_pm_runtime_get(xe);
+ ref = atomic_inc_return(&xe->mem_access.ref);
XE_WARN_ON(ref == S32_MAX);
}
void xe_device_mem_access_put(struct xe_device *xe)
{
- bool hold = xe->mem_access.hold_rpm;
- int ref = atomic_dec_return(&xe->mem_access.ref);
+ int ref;
- if (!ref && hold)
- xe_pm_runtime_put(xe);
+ if (xe_pm_read_callback_task(xe) == current)
+ return;
+
+ ref = atomic_dec_return(&xe->mem_access.ref);
+ xe_pm_runtime_put(xe);
XE_WARN_ON(ref < 0);
}
diff --git a/drivers/gpu/drm/xe/xe_device.h b/drivers/gpu/drm/xe/xe_device.h
index a64828bc6ad2..8b085ffdc5f8 100644
--- a/drivers/gpu/drm/xe/xe_device.h
+++ b/drivers/gpu/drm/xe/xe_device.h
@@ -141,15 +141,8 @@ void xe_device_mem_access_get(struct xe_device *xe);
bool xe_device_mem_access_get_if_ongoing(struct xe_device *xe);
void xe_device_mem_access_put(struct xe_device *xe);
-static inline bool xe_device_mem_access_ongoing(struct xe_device *xe)
-{
- return atomic_read(&xe->mem_access.ref);
-}
-
-static inline void xe_device_assert_mem_access(struct xe_device *xe)
-{
- XE_WARN_ON(!xe_device_mem_access_ongoing(xe));
-}
+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 5267ae02785d..36767b091f8e 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -343,10 +343,14 @@ struct xe_device {
struct {
/** @ref: ref count of memory accesses */
atomic_t ref;
- /** @hold_rpm: need to put rpm ref back at the end */
- 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_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index 9fb5fd4391d2..7200343330fa 100644
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -19,6 +19,7 @@
#include "xe_guc.h"
#include "xe_guc_submit.h"
#include "xe_map.h"
+#include "xe_pm.h"
#include "xe_trace.h"
/* Used when a CT send wants to block and / or receive data */
@@ -1047,9 +1048,11 @@ static void g2h_fast_path(struct xe_guc_ct *ct, u32 *msg, u32 len)
void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
{
struct xe_device *xe = ct_to_xe(ct);
+ bool ongoing;
int len;
- if (!xe_device_mem_access_get_if_ongoing(xe))
+ ongoing = xe_device_mem_access_get_if_ongoing(ct_to_xe(ct));
+ if (!ongoing && xe_pm_read_callback_task(ct_to_xe(ct)) == NULL)
return;
spin_lock(&ct->fast_lock);
@@ -1060,7 +1063,8 @@ void xe_guc_ct_fast_path(struct xe_guc_ct *ct)
} while (len > 0);
spin_unlock(&ct->fast_lock);
- xe_device_mem_access_put(xe);
+ if (ongoing)
+ xe_device_mem_access_put(xe);
}
/* Returns less than zero on error, 0 on done, 1 on more available */
@@ -1091,9 +1095,36 @@ static int dequeue_one_g2h(struct xe_guc_ct *ct)
static void g2h_worker_func(struct work_struct *w)
{
struct xe_guc_ct *ct = container_of(w, struct xe_guc_ct, g2h_worker);
+ bool ongoing;
int ret;
- xe_device_mem_access_get(ct_to_xe(ct));
+ /*
+ * Normal users must always hold mem_access.ref around CT calls. However
+ * during the runtime pm callbacks we rely on CT to talk to the GuC, but
+ * at this stage we can't rely on mem_access.ref and even the
+ * callback_task will be different than current. For such cases we just
+ * need to ensure we always process the responses from any blocking
+ * ct_send requests or where we otherwise expect some response when
+ * initiated from those callbacks (which will need to wait for the below
+ * dequeue_one_g2h()). The dequeue_one_g2h() will gracefully fail if
+ * the device has suspended to the point that the CT communication has
+ * been disabled.
+ *
+ * If we are inside the runtime pm callback, we can be the only task
+ * still issuing CT requests (since that requires having the
+ * mem_access.ref). It seems like it might in theory be possible to
+ * receive unsolicited events from the GuC just as we are
+ * suspending-resuming, but those will currently anyway be lost when
+ * eventually exiting from suspend, hence no need to wake up the device
+ * here. If we ever need something stronger than get_if_ongoing() then
+ * we need to be careful with blocking the pm callbacks from getting CT
+ * responses, if the worker here is blocked on those callbacks
+ * completing, creating a deadlock.
+ */
+ ongoing = xe_device_mem_access_get_if_ongoing(ct_to_xe(ct));
+ if (!ongoing && xe_pm_read_callback_task(ct_to_xe(ct)) == NULL)
+ return;
+
do {
mutex_lock(&ct->lock);
ret = dequeue_one_g2h(ct);
@@ -1107,7 +1138,9 @@ static void g2h_worker_func(struct work_struct *w)
kick_reset(ct);
}
} while (ret == 1);
- xe_device_mem_access_put(ct_to_xe(ct));
+
+ if (ongoing)
+ xe_device_mem_access_put(ct_to_xe(ct));
}
static void guc_ctb_snapshot_capture(struct xe_device *xe, struct guc_ctb *ctb,
diff --git a/drivers/gpu/drm/xe/xe_pm.c b/drivers/gpu/drm/xe/xe_pm.c
index c7901f379aee..fe99820db2df 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)
@@ -210,19 +239,8 @@ 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)
-{
- /* 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;
-}
-
int xe_pm_runtime_get_if_active(struct xe_device *xe)
{
- WARN_ON(pm_runtime_suspended(xe->drm.dev));
return pm_runtime_get_if_active(xe->drm.dev, true);
}
diff --git a/drivers/gpu/drm/xe/xe_pm.h b/drivers/gpu/drm/xe/xe_pm.h
index 8418ee6faac5..da05556d9a6e 100644
--- a/drivers/gpu/drm/xe/xe_pm.h
+++ b/drivers/gpu/drm/xe/xe_pm.h
@@ -19,8 +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);
int xe_pm_runtime_get_if_active(struct xe_device *xe);
void xe_pm_assert_unbounded_bridge(struct xe_device *xe);
+struct task_struct *xe_pm_read_callback_task(struct xe_device *xe);
#endif
--
2.41.0
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