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| /openbmc/linux/arch/s390/kernel/ |
| H A D | processor.c | a9ca8eb7 Sat Feb 28 04:35:26 CST 2015 Heiko Carstens <heiko.carstens@de.ibm.com> s390/ftrace: fix crashes when switching tracers / add notrace to cpu_relax()
With git commit 4d92f50249eb ("s390: reintroduce diag 44 calls for
cpu_relax()") I reintroduced a non-trivial cpu_relax() variant on s390.
The difference to the previous variant however is that the new version is
an out-of-line function, which will be traced if function tracing is enabled.
Switching to different tracers includes instruction patching. Therefore this
is done within stop_machine() "context" to prevent that any function tracing
is going on while instructions are being patched.
With the new out-of-line variant of cpu_relax() this is not true anymore,
since cpu_relax() gets called in a busy loop by all waiting cpus within
stop_machine() until function patching is finished.
Therefore cpu_relax() must be marked notrace.
This fixes kernel crashes when frequently switching between "function" and
"function_graph" tracers.
Moving cpu_relax() to a header file again, doesn't work because of header
include order dependencies.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
a9ca8eb7 Sat Feb 28 04:35:26 CST 2015 Heiko Carstens <heiko.carstens@de.ibm.com> s390/ftrace: fix crashes when switching tracers / add notrace to cpu_relax()
With git commit 4d92f50249eb ("s390: reintroduce diag 44 calls for
cpu_relax()") I reintroduced a non-trivial cpu_relax() variant on s390.
The difference to the previous variant however is that the new version is
an out-of-line function, which will be traced if function tracing is enabled.
Switching to different tracers includes instruction patching. Therefore this
is done within stop_machine() "context" to prevent that any function tracing
is going on while instructions are being patched.
With the new out-of-line variant of cpu_relax() this is not true anymore,
since cpu_relax() gets called in a busy loop by all waiting cpus within
stop_machine() until function patching is finished.
Therefore cpu_relax() must be marked notrace.
This fixes kernel crashes when frequently switching between "function" and
"function_graph" tracers.
Moving cpu_relax() to a header file again, doesn't work because of header
include order dependencies.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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