mainlining shenanigans
2f66196208
cpuinfo_cur_freq gets current CPU frequency as detected by hardware while scaling_cur_freq last known CPU frequency. Some platforms may not allow checking the CPU frequency of an offline CPU or the associated resources may have been released via cpufreq_exit when the CPU gets offlined, in which case the policy would have been invalidated already. If we attempt to get current frequency from the hardware, it may result in hang or crash. For example on Juno, I see: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000188 [0000000000000188] pgd=0000000000000000 Internal error: Oops: 96000004 [#1] PREEMPT SMP Modules linked in: CPU: 5 PID: 4202 Comm: cat Not tainted 4.20.0-08251-ga0f2c0318a15-dirty #87 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform pstate: 40000005 (nZcv daif -PAN -UAO) pc : scmi_cpufreq_get_rate+0x34/0xb0 lr : scmi_cpufreq_get_rate+0x34/0xb0 Call trace: scmi_cpufreq_get_rate+0x34/0xb0 __cpufreq_get+0x34/0xc0 show_cpuinfo_cur_freq+0x24/0x78 show+0x40/0x60 sysfs_kf_seq_show+0xc0/0x148 kernfs_seq_show+0x44/0x50 seq_read+0xd4/0x480 kernfs_fop_read+0x15c/0x208 __vfs_read+0x60/0x188 vfs_read+0x94/0x150 ksys_read+0x6c/0xd8 __arm64_sys_read+0x24/0x30 el0_svc_common+0x78/0x100 el0_svc_handler+0x38/0x78 el0_svc+0x8/0xc ---[ end trace 3d1024e58f77f6b2 ]--- So fix the issue by checking if the policy is invalid early in __cpufreq_get before attempting to get the current frequency. Signed-off-by: Sudeep Holla <sudeep.holla@arm.com> Acked-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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 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.