Corey,
On Thu, Jan 8, 2009 at 8:58 PM, Corey Ashford <cjash...@linux.vnet.ibm.com> wrote: > 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!). > I remember that problem and I thought you had a patch already. Did I forget to apply it? > 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. > Looks like the problem is related to the calling convention and caller vs. callee save registers. The proposed patch work around the problem, the real fix would be to save and restore the r4 register which appears to be a caller save. But I'll take the patch for now. ------------------------------------------------------------------------------ Check out the new SourceForge.net Marketplace. It is the best place to buy or sell services for just about anything Open Source. http://p.sf.net/sfu/Xq1LFB _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
