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Srinivas Pandruvada a1850e2aef cpufreq: intel_pstate: Fix crash during turbo disable 
commit 6b050482ec upstream.

When the system is booted with kernel command line argument "nosmt" or
"maxcpus" to limit the number of CPUs, disabling turbo via:

 echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo

results in a crash:

 PF: supervisor read access in kernel mode
 PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: Oops: 0000 [#1] SMP PTI
 ...
 RIP: 0010:store_no_turbo+0x100/0x1f0
 ...

This occurs because for_each_possible_cpu() returns CPUs even if they
are not online. For those CPUs, all_cpu_data[] will be NULL. Since
commit 973207ae3d ("cpufreq: intel_pstate: Rearrange max frequency
updates handling code"), all_cpu_data[] is dereferenced even for CPUs
which are not online, causing the NULL pointer dereference.

To fix that, pass CPU number to intel_pstate_update_max_freq() and use
all_cpu_data[] for those CPUs for which there is a valid cpufreq policy.

Fixes: 973207ae3d ("cpufreq: intel_pstate: Rearrange max frequency updates handling code")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221068
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: 6.16+ <stable@vger.kernel.org> # 6.16+
Link: https://patch.msgid.link/20260225001752.890164-1-srinivas.pandruvada@linux.intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-03-12 07:09:40 -04:00
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README 

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 reStructuredText 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.