Hello,
It appears that I have forgotten to post a patch for this bug. This was
a problem I had seen when booting the latest 2.6.28-rc6 kernel, where
kernel function tracing was causing r4 to be corrupted because the
perfmon code was called in the wrong order (pretty obscure bug!).
To elabortate just a little, this is assembler code where do_signal is
called with two register parameters - r3 and r4. r4 is set up several
lines before the call to do_signal and is easy to miss. The call to the
perfmon function, pfm_handle_work, doesn't have a second parameter, but
if in the process of calling pfm_handle_work, r4 changes (perhaps
because it calls a function with 2 or more register parameters), when
the subseqent call to do_signal is made, r4 will be corrupted. With
kernel tracing turned on, r4 was getting touched in the process of
calling pfm_handle_work, causing do_signal to cause the system to hang.
In order to fix this, the simplest thing to do was to reverse the order
of the two calls so that no saving of r4 was needed. pfm_handle_work is
now called after do_signal, eliminating any possibility for corruption
of parameter registers.
Please let me know if there are any issues with this patch.
Regards,
- Corey
Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjash...@us.ibm.com
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index a6478a9..a50668e 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -654,12 +654,12 @@ user_work:
b .ret_from_except_lite
1: bl .save_nvgprs
+ addi r3,r1,STACK_FRAME_OVERHEAD
+ bl .do_signal
#ifdef CONFIG_PERFMON
addi r3,r1,STACK_FRAME_OVERHEAD
bl .pfm_handle_work
#endif /* CONFIG_PERFMON */
- addi r3,r1,STACK_FRAME_OVERHEAD
- bl .do_signal
b .ret_from_except
unrecov_restore:
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