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04ad505eed
The following deadlock exists in i915_active_wait() due to a double lock on ref->mutex (call chain listed in order from top to bottom): i915_active_wait(); mutex_lock_interruptible(&ref->mutex); <-- ref->mutex first acquired i915_active_request_retire(); node_retire(); active_retire(); mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); <-- DEADLOCK Fix the deadlock by skipping the second ref->mutex lock when active_retire() is called through i915_active_request_retire(). Note that this bug only affects 5.4 and has since been fixed in 5.5. Normally, a backport of the fix from 5.5 would be in order, but the patch set that fixes this deadlock involves massive changes that are neither feasible nor desirable for backporting [1][2][3]. Therefore, this small patch was made to address the deadlock specifically for 5.4. [1]274cbf20fd("drm/i915: Push the i915_active.retire into a worker") [2]093b922873("drm/i915: Split i915_active.mutex into an irq-safe spinlock for the rbtree") [3]750bde2fd4("drm/i915: Serialise with remote retirement") Fixes:12c255b5da("drm/i915: Provide an i915_active.acquire callback") Cc: <stable@vger.kernel.org> # 5.4.x Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.