Date: Fri, 19 Apr 2013 11:53:22 -0700 From: Carl Shapiro <carl.shapiro@gmail.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: MADV_FREE and wait4 EFAULT Message-ID: <CANVK_Qjsa8-%2BtELi--Z6QttxhbkzxTQ1_aGyz=BGcYh3ng2qfw@mail.gmail.com> In-Reply-To: <20130419124942.GA67273@kib.kiev.ua> References: <CANVK_QgKRkpzWjA=H2u2HTp_vpxFhNLBGTVuFZmMEpBLTbzeaA@mail.gmail.com> <20130417082143.GW2930@kib.kiev.ua> <CANVK_QgRBO5ZU=NHCr1XTvtxYpWk6LjWEv8Q-70mY6CzqHO2TA@mail.gmail.com> <20130419124942.GA67273@kib.kiev.ua>
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On Fri, Apr 19, 2013 at 5:49 AM, Konstantin Belousov <kostikbel@gmail.com>wrote: > It would be of some interest to see the evidence. > Certainly. Here is some of the debugging messages that I added to my application. The first line is a print statement that executes after the system call returns. (As an aside, we issue system calls directly and do not link against the C library.) The other 2 lines of interest are output from the dump of /proc/curproc/map that correspond to the status and rusage addresses. wait4 returned EFAULT, status is 0xc20021c0e8 rusage is 0xc2000eaf30 ... 0xc1ffff0000 0xc200100000 245 0 0xfffffe07cd9ebbc8 rw- 1 0 0x3000 COW NNC default - CH 1001 ... 0xc200200000 0xc200300000 250 0 0xfffffe0215e3ed98 rw- 1 0 0x3000 COW NNC default - CH 1001 I realize this might not be satisfying but I am happy to provide any other information you might be interested in. Is your code multithreaded ? > Yes. The test case is required to decide whether the bug is in the application > or in the OS. > To be clear, I do not have a strong reason to believe there bug is in FreeBSD. My original enquiry was solely into whether we were misusing MADV_FREE pages. However, the wait4 failure is very suspicious because the only two addresses written to are "out" parameters. > There is no difference in the access performed by copyout vs. access > caused > by the usermode write. > Thanks. > No, I cannot give an advice, I think we should first decide which code > to blame. > Well, I have a strong suspicion the problem is caused by my application for the reasons mentioned above. > BTW, you could try enabling sysctl machdep.uprintf_signal. This does not seem to be available in my kernel but I could patch this change... http://svnweb.freebsd.org/base/head/sys/amd64/amd64/trap.c?r1=239251&r2=239252&; ...and it looks like I need to rebuild my kernel anyway to enable DTrace. > Oh, you did not > specified the architecture and version of the system. Sorry, here is what "uname -mv" says FreeBSD 9.1-RELEASE #0 r243825: Tue Dec 4 09:23:10 UTC 2012 root@farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64
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