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In commit86aa7e760a("drm/i915: Assert that the context-switch completion matches our context") I added a read to the irq tasklet handler that compared the on-chip status with that of our sw tracking, using an unguarded read of the request pointer to get the context and beyond. Whilst we hold a reference to the request, we do not hold anything on the context and if we are unlucky it may be reaped from a second thread retiring the request (since it may retire the request as soon as the breadcrumb is complete, even before we finish processing the context switch) as we try to read from the context pointer. Avoid the racy read from underneath the request by storing the expected result in the execlist_port[]. v2: Include commentary about port[].request being unprotected. Fixes:86aa7e760a("drm/i915: Assert that the context-switch completion matches our context") Reported-by: Mika Kuoppala <mika.kuoppala@intel.com> Testcase: igt/gem_ctx_create Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20170206170502.30944-2-chris@chris-wilson.co.uk
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.