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0e00a8814e
Avoid the following lockdep complaint: <4> [298.856498] ====================================================== <4> [298.856500] WARNING: possible circular locking dependency detected <4> [298.856503] 6.7.0-rc5-CI_DRM_14017-g58ac4ffc75b6+ #1 Tainted: G N <4> [298.856505] ------------------------------------------------------ <4> [298.856507] kworker/4:1H/190 is trying to acquire lock: <4> [298.856509] ffff8881103e9978 (>->reset.backoff_srcu){++++}-{0:0}, at: _intel_gt_reset_lock+0x35/0x380 [i915] <4> [298.856661] but task is already holding lock: <4> [298.856663] ffffc900013f7e58 ((work_completion)(&(&guc->timestamp.work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x264/0x530 <4> [298.856671] which lock already depends on the new lock. The complaint is not actually valid. The busyness worker thread does indeed hold the worker lock and then attempt to acquire the reset lock (which may have happened in reverse order elsewhere). However, it does so with a trylock that exits if the reset lock is not available (specifically to prevent this and other similar deadlocks). Unfortunately, lockdep does not understand the trylock semantics (the lock is an i915 specific custom implementation for resets). Not doing a synchronous flush of the worker thread when a reset is in progress resolves the lockdep splat by never even attempting to grab the lock in this particular scenario. There are situatons where a synchronous cancel is required, however. So, always do the synchronous cancel if not in reset. And add an extra synchronous cancel to the end of the reset flow to account for when a reset is occurring at driver shutdown and the cancel is no longer synchronous but could lead to unallocated memory accesses if the worker is not stopped. Signed-off-by: Zhanjun Dong <zhanjun.dong@intel.com> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> Cc: Andi Shyti <andi.shyti@linux.intel.com> Cc: Daniel Vetter <daniel@ffwll.ch> Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20231219195957.212600-1-John.C.Harrison@Intel.com |
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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.