[Webkit-unassigned] [Bug 237758] New: GBMDevice as a thread-specific object is problematic
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Fri Mar 11 00:38:45 PST 2022
https://bugs.webkit.org/show_bug.cgi?id=237758
Bug ID: 237758
Summary: GBMDevice as a thread-specific object is problematic
Product: WebKit
Version: WebKit Nightly Build
Hardware: Unspecified
OS: Unspecified
Status: NEW
Severity: Normal
Priority: P2
Component: New Bugs
Assignee: webkit-unassigned at lists.webkit.org
Reporter: zan at falconsigh.net
Blocks: 237649
GBMDevice, and the gbm_device instance it wraps, can cause problems when managed on a thread-specific basis. gbm_bo objects created through these devices can be shipped or used across different threads, but it can also happen that the thread on which they were created through the GBMDevice/gbm_device specific to that thread is destroyed while gbm_bo objects live on. So the gbm_device is destroyed but the gbm_bo objects created through it live on, causing problems when the gbm_bo instance tries to use now-destroyed gbm_device for different operations.
This is happening under certain circumstances inside GStreamer integration along with the swapchain object (bug #237238). Swapchain remains the same for the duration of the MediaPlayerPrivateGStreamer's lifetime. During the first playback, GStreamer's pipeline handles playback on one thread, spawning gbm_bo objects as required given that thread's GBMDevice. Once playback finishes, the pipeline will deconstruct these threads and the GBMDevice, which leaves the swapchain objects with a dangling gbm_device pointer.
Mesa's libgbm is a useful wrapper along the specified DRI device file descriptor. I don't see possible thread-safety issues there, or at least have not experienced them so far working with that library. There's other implementations (closed-source too) that might not be so generous, but I would presume thread safety first. If things go sideways there's options of having a libgbm-specific thread where these allocations are performed, but the basis even before that would be a single per-process gbm_device.
Referenced Bugs:
https://bugs.webkit.org/show_bug.cgi?id=237649
[Bug 237649] [Meta][Linux] Adoption of DMABuf as a reference buffer sharing mechanism
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