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[ Upstream commit 2b038cbc5f ]
When booting a pseries kernel with PREEMPT enabled, it dumps the
following warning:
BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
caller is pseries_processor_idle_init+0x5c/0x22c
CPU: 13 PID: 1 Comm: swapper/0 Not tainted 4.20.0-rc3-00090-g12201a0128bc-dirty #828
Call Trace:
[c000000429437ab0] [c0000000009c8878] dump_stack+0xec/0x164 (unreliable)
[c000000429437b00] [c0000000005f2f24] check_preemption_disabled+0x154/0x160
[c000000429437b90] [c000000000cab8e8] pseries_processor_idle_init+0x5c/0x22c
[c000000429437c10] [c000000000010ed4] do_one_initcall+0x64/0x300
[c000000429437ce0] [c000000000c54500] kernel_init_freeable+0x3f0/0x500
[c000000429437db0] [c0000000000112dc] kernel_init+0x2c/0x160
[c000000429437e20] [c00000000000c1d0] ret_from_kernel_thread+0x5c/0x6c
This happens because the code calls get_lppaca() which calls
get_paca() and it checks if preemption is disabled through
check_preemption_disabled().
Preemption should be disabled because the per CPU variable may make no
sense if there is a preemption (and a CPU switch) after it reads the
per CPU data and when it is used.
In this device driver specifically, it is not a problem, because this
code just needs to have access to one lppaca struct, and it does not
matter if it is the current per CPU lppaca struct or not (i.e. when
there is a preemption and a CPU migration).
That said, the most appropriate fix seems to be related to avoiding
the debug_smp_processor_id() call at get_paca(), instead of calling
preempt_disable() before get_paca().
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.