On Tue, Apr 16, 2013 at 02:12:54PM -0700, Carl Shapiro wrote: > I am seeing wait4 system calls failing with an EFAULT and I am trying to > understand what might be going wrong. > > An inspection of the wait4 implementation suggests the opportunity for > EFAULT is within its invocations of copyout. In my situation, the status > and rusage pointer arguments contain addresses to mmaped pages which have > been madvised as MADV_FREE. > > Is it permissible to pass pages which have been madvised MADV_FREE to wait4 > or any other system call for that matter? Might there be another > opportunity for a wait4 to EFAULT?
Did you ensured with e.g. ktrace and procstat -v that your assumptions hold, i.e. the addresses supplied as wait4(2) arguments are valid ? Please provide the minimal test case demonstrating the behaviour. MADV_FREE should only result in the possible lost of the previous content of the page, not in the faulting of the page access. From the inspection of the code, I do not see how MADV_FREE could result in the memory address becoming invalid.
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