6.12-stable review patch. If anyone has any objections, please let me know.
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From: Zbigniew Kempczyński zbigniew.kempczynski@intel.com
[ Upstream commit 04e1f683cd28dc9407b238543871a6e09a570dc0 ]
Marking ufence as signalled after copy_to_user() is too late. Worker thread which signals ufence by memory write might be raced with another userspace vm-bind call. In map/unmap scenario unmap may still see ufence is not signalled causing -EBUSY. Change the order of marking / write to user-fence fixes this issue.
Fixes: 977e5b82e090 ("drm/xe: Expose user fence from xe_sync_entry") Link: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5536 Signed-off-by: Zbigniew Kempczyński zbigniew.kempczynski@intel.com Cc: Matthew Brost matthew.brost@intel.com Cc: Matthew Auld matthew.auld@intel.com Reviewed-by: Matthew Brost matthew.brost@intel.com Signed-off-by: Matthew Brost matthew.brost@intel.com Link: https://lore.kernel.org/r/20250820083903.2109891-2-zbigniew.kempczynski@inte... (cherry picked from commit 8ae04fe9ffc93d6bc3bc63ac08375427d69cee06) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/xe/xe_sync.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/xe/xe_sync.c b/drivers/gpu/drm/xe/xe_sync.c index b0684e6d2047b..dd7bd766ae184 100644 --- a/drivers/gpu/drm/xe/xe_sync.c +++ b/drivers/gpu/drm/xe/xe_sync.c @@ -77,6 +77,7 @@ static void user_fence_worker(struct work_struct *w) { struct xe_user_fence *ufence = container_of(w, struct xe_user_fence, worker);
+ WRITE_ONCE(ufence->signalled, 1); if (mmget_not_zero(ufence->mm)) { kthread_use_mm(ufence->mm); if (copy_to_user(ufence->addr, &ufence->value, sizeof(ufence->value))) @@ -89,7 +90,6 @@ static void user_fence_worker(struct work_struct *w) * Wake up waiters only after updating the ufence state, allowing the UMD * to safely reuse the same ufence without encountering -EBUSY errors. */ - WRITE_ONCE(ufence->signalled, 1); wake_up_all(&ufence->xe->ufence_wq); user_fence_put(ufence); }