drm/tests: shmem: Hold reservation lock around purge

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/tests: shmem: Hold reservation lock around purge Acquire and release the GEM object's reservation lock around calls to the object's purge operation. The tests use drm_gem_shmem_purge_locked(), which led to errors such as show below. [ 58.709128] WARNING: CPU: 1 PID: 1354 at drivers/gpu/drm/drm_gem_shmem_helper.c:515 drm_gem_shmem_purge_locked+0x51c/0x740 Only export the new helper drm_gem_shmem_purge() for Kunit tests. This is not an interface for regular drivers.

References

• https://git.kernel.org/stable/c/cdf8bbbd9017adcfb91ad9a902198d4b507719a9
• https://git.kernel.org/stable/c/8baeee2c1c0cdb3a8eac3b8f38156cce6ee1a69f
• https://git.kernel.org/stable/c/3f41307d589c2f25d556d47b165df808124cd0c4