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f4c0a7999f
commit 2468b0e3d5659dfde77f081f266e1111a981efb8 upstream.
When CONFIG_PREEMPT_COUNT is not configured (i.e. CONFIG_PREEMPT_NONE/
CONFIG_PREEMPT_VOLUNTARY), preempt_disable() / preempt_enable() merely
acts as a barrier(). However, in these cases cond_resched() can still
trigger a context switch and modify the CSR.EUEN, resulting in do_fpu()
exception being activated within the kernel-fpu critical sections, as
demonstrated in the following path:
dcn32_calculate_wm_and_dlg()
DC_FP_START()
dcn32_calculate_wm_and_dlg_fpu()
dcn32_find_dummy_latency_index_for_fw_based_mclk_switch()
dcn32_internal_validate_bw()
dcn32_enable_phantom_stream()
dc_create_stream_for_sink()
kzalloc(GFP_KERNEL)
__kmem_cache_alloc_node()
__cond_resched()
DC_FP_END()
This patch is similar to commit d02198550423a0b (x86/fpu: Improve crypto
performance by making kernel-mode FPU reliably usable in softirqs). It
uses local_bh_disable() instead of preempt_disable() for non-RT kernels
so it can avoid the cond_resched() issue, and also extend the kernel-fpu
application scenarios to the softirq context.
Cc: stable@vger.kernel.org
Signed-off-by: Tianyang Zhang <zhangtianyang@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
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.