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vcpu_is_preempted() can be used outside of preempt-disabled critical
sections, yielding warnings such as:
BUG: using smp_processor_id() in preemptible [00000000] code: systemd-udevd/185
caller is rwsem_spin_on_owner+0x1cc/0x2d0
CPU: 1 PID: 185 Comm: systemd-udevd Not tainted 5.15.0-rc2+ #33
Call Trace:
[c000000012907ac0] [c000000000aa30a8] dump_stack_lvl+0xac/0x108 (unreliable)
[c000000012907b00] [c000000001371f70] check_preemption_disabled+0x150/0x160
[c000000012907b90] [c0000000001e0e8c] rwsem_spin_on_owner+0x1cc/0x2d0
[c000000012907be0] [c0000000001e1408] rwsem_down_write_slowpath+0x478/0x9a0
[c000000012907ca0] [c000000000576cf4] filename_create+0x94/0x1e0
[c000000012907d10] [c00000000057ac08] do_symlinkat+0x68/0x1a0
[c000000012907d70] [c00000000057ae18] sys_symlink+0x58/0x70
[c000000012907da0] [c00000000002e448] system_call_exception+0x198/0x3c0
[c000000012907e10] [c00000000000c54c] system_call_common+0xec/0x250
The result of vcpu_is_preempted() is always used speculatively, and the
function does not access per-cpu resources in a (Linux) preempt-unsafe way.
Use raw_smp_processor_id() to avoid such warnings, adding explanatory
comments.
Fixes: ca3f969dcb ("powerpc/paravirt: Use is_kvm_guest() in vcpu_is_preempted()")
Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210928214147.312412-3-nathanl@linux.ibm.com
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.