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diff --git a/open_issues/sigpipe.mdwn b/open_issues/sigpipe.mdwn new file mode 100644 index 00000000..0df3560e --- /dev/null +++ b/open_issues/sigpipe.mdwn @@ -0,0 +1,345 @@ +[[!meta copyright="Copyright © 2011 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_glibc open_issue_hurd]] + +[[!GNU_Savannah_bug 461]] + +IRC, freenode, #hurd, 2011-04-20 + + <svante_> I found a problem from 2002 by Marcus Brinkmann that I think is + related to my problems: http://savannah.gnu.org/bugs/?461. He has a test + file called pipetest.c that shows that SIGPIPE is not triggered reliably. + <svante_> Cited from the bug report: The attached test program does not + trigger SIGPIPE reliably, because closing the read end of the pipe + happens asynchronously. The write can succeed because the read end might + not have been closed yet. + <svante_> I have debugged this program on both Hurd and Linux, and the + problem in Hurd remains:-( + <svante_> Anybody looked into the almost ten year old + bug:http://savannah.gnu.org/bugs/?461 this one is definitely related to + the build problems of e.g. ghc6 and ruby1.9.1. Should I mention this on + the ML? + <youpi> that could be it indeed + <youpi> does th bug still happen? + <azeem> depends on: new interface io_close + <azeem> which depends on: POSIX record locking + <svante_> youpi: Yes it does, I've tested the pipetest.c file submitted by + Marcus B on both Linux and Hurd + <azeem> that would've maybe been a nice GSOC task + <youpi> azeem: err, the contrary for posix record locking, non ? + <azeem> argh + <azeem> why would POSIX record locking depend on this? + <azeem> well anyway, then have POSIX record locking be a GSOC task :) + <azeem> I wasn't aware that would also fix ruby and ghc building :) + <youpi> http://permalink.gmane.org/gmane.os.hurd.devel.readers/265 + <youpi> (for io_close stuff) + <youpi> http://comments.gmane.org/gmane.os.hurd.devel.readers/63 actually + <azeem> I guess if they didn't implement it/agreed on something back then + it'd be quite hard to do it now + <svante_> azeem: marcus recently showed up here. Maybe he can help out/has + ideas? + <azeem> well yeah + <azeem> but marcus was the junior guy back then + <azeem> <marcus> but it's a very hurdish solution (ie, complex, buggy, and + not implemented) + <azeem> maybe we can go for something simpler + <youpi> azeem: what is this quote about? + <azeem> don't remember + <azeem> not io_close I'd say + +2011-04-21 + + <antrik> svante_: why do you think the problem you see in ruby and ghc is + related to async close() ? + +2011-04-22 + + <svante_> Well: the test case I'm running on ruby is giving me an EBADF + after 8 successful loops, and tracing within eglibc points towards + __mutex_lock_solid or __spin_lock, __spin_lock_solid from + mach/lock-intern.h from cthreads. + +2011-04-23 + + <antrik> srs1: yeah, I saw it... but I still wonder what makes you think + this is related to async FD closing? + <srs1> antrik: Every test case showing the problems are related to fd.h and + the functions there, especially the ones used in the function: + _HURD_FD_H_EXTERN_INLINE struct hurd_fd *_hurd_fd_get (int fd) and so is + the pipetest from Marcus too. + <srs1> I have not yet been able to trace further with gdb since most + variables are optimized out and adding print statements does not work, at + least not yet. Now I'm trying to build eglibc with -O1 to see if the + optimized out variables are there or not. + <youpi> srs1: he means the ghc6 issue + <youpi> (and the ruby issue) + <srs1> youpi: Yes, the ghc6 and ruby ends at the functions I mentioned in + fd,h + <srs1> Both ghc6 and ruby programs are writing to a file when the error + happens. If they are using a pipeline or not I don't know yet, I think it + is a regular file write. + <srs1> I can send your the ruby program if you like: It is a c-file so + debugging is possible. ghc6 is worse, since that program cannot be + debugged directly with gdb. + <antrik> pipetest also results in the program hanging in locking stuff?... + <srs1> pipetest does not hang, but gives no output as it should. Running it + in gdb with single stepping shows the correct behavior, but then gdb + hangs if I try to single stepping further, continue at the right place + works! + <antrik> I haven't looked at the pipetest program. do you have the link + handy? + <antrik> never mind, got it + <antrik> srs1: that sounds like a GDB problem... + <youpi> most probably, yes + <youpi> (and I've always seen issues like this in gdb on hurd) + <antrik> actually I think it's expected... the RPC handling code has some + explicit GDB hooks AIUI; trying to single-step into this code is probably + expected to wreck havoc... + <youpi> well, it should have some sane behavior + <youpi> even if it's "skip to next point where it's debuggable" + <antrik> srs1: note that there is no BADF involved in the pipetest AIUI... + +2011-04-28 + + <antrik> what is the actual problem you are seeing BTW? + <gnu_srs1> antrik: in ruby the problem is: Exception `IOError' at + tool/mkconfig.rb:12 - closed stream + <gnu_srs1> Triggered by ruby:io.c:internal_read_func() calling + sysdeps/mach/hurd/read.c returning a negative number of bytes read. + <abeaumont> gnu_srs1: why do you think that error is locking related? + <gnu_srs1> This happens after 8 iterations of the read loop with 8192 bytes + read each time. + <abeaumont> but that doesn't involve locking at all, does it? + <gnu_srs1> I think it is, if there is a pipepline set up?? + <gnu_srs1> Also the ghc6 hang ends up in hangs in sysdeps/mach/hurd/read.c + traced into fd.h where all things happen (including setting locks and + mutexes) + <braunr> what locking ? + <braunr> stdio locking is different from file locking + <braunr> and a pipe doesn't imply file locking at all + <abeaumont> read may block on pipes, but it's unrelated to flock + <gnu_srs1> Look into the file fd.h, maybe you can describe things + better. I'm not fluent in this stuff. + <gnu_srs1> Has a pipe has a file descriptor associated to it? What about a + file read/write? + <abeaumont> a pipe provides 2 file descriptors, one for reading and another + one for writting + <abeaumont> i may give a look at that if i manage to build glibc + succesfully... + <gnu_srs1> Take a look at the realevant code from fd.h: + http://pastebin.com/kesBpjy4 + <abeaumont> the ruby error happens just trying to build ruby1.9? + <abeaumont> gnu_srs1: from what you said, the error occurs while reading, + so i don't see how it can be related to that code + <abeaumont> you already got a descriptor if you're reading from it + <gnu_srs1> I have not tried anything else than ruby1.9.1. I can send you + the ruby debug setup and files if you are interested. + <abeaumont> gnu_srs1: ok, i'll try to build ruby1.9.1 later... let's see if + i can build glibc first + <gnu_srs1> abeaumont: well, the read suddenly returns -1 bytes read, + resulting in a file descriptor of -1 (instead of +3). + <abeaumont> gnu_srs1: i see + <antrik> gnu_srs1: are you sure the hang really happens in _hurd_fd_get()? + could you give us a backtrace? + <antrik> gnu_srs1: there are many reasons why read() can return -1; errno + should indicate the reason. unfortunately, I can't make much out of + ruby's "translation" of the error :-) + <gnu_srs1> antrik: In the ruby case there is no hang: The steam is closed + by read() giving an error code !=0. This triggers things in the ruby + code: A negative number of bytes read and a negative fd results, and an + error error is triggered in the ruby code. + <gnu_srs1> antrik: See http://pastebin.com/eZmaZQJr + <antrik> gnu_srs1: yes, this all sounds perfectly right. the question is + *why* read() returns an error code. we'd need to know what error it is + exactly, and in what situation it occurs. tracing the libc code is not at + all useful here + <antrik> uhm... 1073741833 is errno?... + <gnu_srs1> BTW: I think the error code is EBADF (badfile descriptor?). The + integer version of it is 1073741833, see the pastebin i linked to. + <antrik> you could use perror() to get something more readable :-) + <antrik> or error() with the right arguments + <gnu_srs1> I used integer when printing, but looking into fd.h I think it + is EBADF (I did get this result once in gdb) + <antrik> fd.h won't tell you anything. most error codes are generated by + the server, not by libc + <antrik> BADF might be generated in libc when ruby tries to read on FD -1 + <antrik> (no idea why it tries to do that... perhaps there is actually + something wrong/stupid in ruby's error handling) + <gnu_srs1> Well I single-stepped in fd.h using gdb and printing err gave + EBADf. err is declared as: error_t err in read.c + <antrik> at which point did you single-step? while fd was still 3? + <gnu_srs1> I don't think the problem is in ruby, it is in mach/hurd! + Similar problems with ghc, python-apt, etc + <gnu_srs1> Yes, fd=3 was not changed. I cannot trace into fd.h from + read.c. That is the problem with all cases! Need to leave for a while + now. + <antrik> sorry, I don't see *anything* similar in the ghc failure. + <antrik> I don't know about python-apt + <antrik> for the ghc case, I'd like to see a GDB backtrace from the point + where it is hanging + <antrik> just to be clear: anything I/O-related will involve fd.h + somewhere. that doesn't in any way indicate the problems are related. in + fact the symptoms you described are very different, and I'm pretty + certain these are completely different issues + <gnu_srs1> antrik: Here is a backtrace, + http://pastebin.com/wvCiXFjB. Numbers 6,7,8 are from the calling Haskell + functions. They cannot be debugged by gdb. Nice to see that somebody is + showing interest at last:-/ + <antrik> hm... I wonder whether the _hurd_intr_rpc_msg_in_trap is a result + of the ^C? + <antrik> if so, it seems to be a "normal" bloking read() operation. so + again probably not related to libc code at all + <gnu_srs1> Where is this blocking read() code located mach/hurd? + <antrik> io_read() is implemented by whatever server handles the FD in + question + <antrik> I guess rpctrace will be more helpful here than GDB... to see what + the program is trying to do here + <gnu_srs1> Why don't I get there with gdb? + <antrik> err... the server is a different process + <antrik> you are only tracing the client code + <gnu_srs1> OK, here is a rpctrace for ruby: + http://pastebin.com/sdPiKGBW.Nice programs you have, no manual pages, and + the program hang + <gnu_srs1> s/http://pastebin.com/sdPiKGBW.Nice + /http://pastebin.com/sdPiKGBW. BTW: Nice/ + <gnu_srs1> antrik: Do you want the rpctrace of the ghc hang too? If that is + the case, do you need the whole file. From the ruby case the last part + looked most interesting: + libpthread/sysdeps/generic/pt-mutex-timedlock.c: assert (mutex->owner != + self); + <antrik> gnu_srs1: hm... you get that assertion only with rpctrace? guess + it doesn't work properly then :-( + <gnu_srs1> Is it visible on the client side? + <antrik> gnu_srs1: that assertion *is* from the client side. I'm just + surprised that apparently it's only triggered when you run it in rpctrace + <antrik> how did you invoke rpctrace? + <gnu_srs1> rpctrace "command with options" > rpctrace.out 2>&1 + <antrik> well, I'd like to know the "command with options" part :-) + <gnu_srs1> OK: for ruby: ./miniruby ./ tool/mkconfig.rb as before. + <antrik> OK, so it just runs the ruby interpreter and no other processes + <gnu_srs1> No other processes involved! + <abeaumont> gnu_srs1: i can reproduce the ruby error, no let's dig in it :D + <antrik> gnu_srs1: rpctrace for ghc could be useful too... but if it's too + long, pasting only the last bit might suffice + <gnu_srs1> antrik: OK, will do that. Do you find anything interesting? + <gnu_srs1> abeaumont: Using gdb: gdb ./miniruby; (gdb) break io.c:569; c8; + break fd.h:72 or break read.c:27 and you are there. Beware of gdb + hanging, so you need another terminal to kill -9 gdb (sometimes a reboot + is needed :-( + <antrik> gnu_srs1: no, the ruby rpctrace is useless; apparently rpctrace + makes it break before reaching the relevant part :-( + <abeaumont> thanks gnu_srs1 + <gnu_srs1> antrik: Hope for better luck with ghc: + http://pastebin.com/dgcrA05t + <antrik> hm... it hangs at proc_dostop() again... whatever that means + +2011-05-07 + + <gnu_srs> One question about ruby: I know where the problems occur in ruby + code. Can I switch to the kernel thread just before in gdb to single step + from there? + <youpi> you can put a breakpoint, can't you? + <antrik> gnu_srs: kernel thread? + <gnu_srs> Yes, but will single stepping from there lead me to the Hurd + code. I have not succeeded to do that yet! + <youpi> you mean the translator code? + <gnu_srs> Well, Roland did call it the signal thread, there are at least + two threads per process, a signal thread and a main (user) thread. + <youpi> then it's a thread in gdb + <youpi> just use the thread gdb commands to access it + <gnu_srs> I do find two threads in gdb, yes. But following only the user + thread does not lead me to the cause of the problems. + <gnu_srs> And following the other (signal thread) has not been successful + so far. + <youpi> multithreading debugging in gdb is painful yes + <youpi> single-step isn't really an option in it + <antrik> gnu_srs: well, as I said before, the cause is probably not in the + libc code anyways. it would be much more relevant to find out what the FD + in question is, and what "special" thing Ruby does to it to trigger the + problematic behaviour... + <youpi> it's simpler to put printfs etc. + <antrik> youpi: well, printf doesn't work in the FD code :-) + <youpi> you can make it work + <youpi> open /dev/mem, write to 0xb8000 + <youpi> I'm not even joking + <gnu_srs> I have printfs in the ruby code. And at some parts in eglibc (but + it is not possible to put them at all places I want, as mentioned before) + <antrik> sure, there are ways to debug this code too... but I don't think + it's useful. so far there is no indication that this will help finding + the actual issue + <gnu_srs> The problem is not file descriptors. It is that an ongoing read + suddenly returns -1 bytes read. And then the ruby code assigns a negative + file descriptor in the exception handling. + <youpi> a *read* ? + <youpi> with errno == 0 ? + <gnu_srs> Yes, a read! + <youpi> how ruby comes to assigning a negative fd from that? + <youpi> does it somehow close the fd? + <gnu_srs> The errno reported from the read is EBADF! + <youpi> did you try to rpctrace it? + <gnu_srs> I don't bother too much about ruby exception handling. The error + has already happened in the read operation. And that lead me to eglibc + code.... and so on... + <youpi> do you know what kind of file this fd was supposed to be on? + <youpi> sure, that's debugging + <gnu_srs> Yes I did rpctrace, but that was not successful. rpctrace just + hang! Buggy code? + <antrik> youpi: I assume that's Ruby's way to indicate that the FD is not + valid anymore, after the previous error + <youpi> does the program fork? + <youpi> antrik: possibly + <youpi> rpctrace has known issues, yes + <youpi> gnu_srs: did you trace close()s by hand with printfs? + <gnu_srs> Ho w to find out if it forks? + <youpi> what does rpctrace stop on ? + <gnu_srs> Well, I don't remember. Antrik? + <antrik> proc_dostop() IIRC + <antrik> or something like that + <gnu_srs> I did not find any close() statements in the code I debugged. + <youpi> ok, proc_dostop() is typically a sign of fork() + <youpi> gnu_srs: that doesn't necessarily mean it's not called + <antrik> gnu_srs: I think his point is that something else might close the + FD, causing the error you see + <youpi> anything can happen in the wild :) + <antrik> gnu_srs: as I said before, the next step is to find out what this + FD is, and what happens to it... + <gnu_srs> antrik: Any ideas how to find out? + <youpi> what is the backtrace? + <gnu_srs> Well I know the fd number, it is either 3 or 5 in my tests. Does + the number matter? + <youpi> yes, it's not std{in,out,err} + <gnu_srs> How to get a backtrace of a program that does not hang? + <youpi> make it hang at the point of failure + <youpi> when read returns -1 + <youpi> so you know who did the read + <gnu_srs> I have to run the loop several times before the number of bytes + read is -1. + <youpi> you mean running the program several times ? + <youpi> or just let the loop continue for some time? + <pinotree> if it's the latter, you can add breakpoints with conditions + <gnu_srs> No the read loop runs for 7 iterations, and fails the 8th time! + <youpi> then make it hang when read() returns -1 + <Mr_Spock> could you paste your code somewhere? + <youpi> when debugging, you're allowed to do all kinds of ugly things, you + know ;) + <gnu_srs> OK, I'll try that. + <gnu_srs> MR_Spock: The easiest way would be to try to build + ruby1.9.1. Then I can help you from where it fails. + <gnu_srs> pinotree: How to give a breakpoint with a condition? + <pinotree> break where if condition + <youpi> see help break + <youpi> oh, there's even a thread condition nowadays, good + <gnu_srs> Thanks for the discussion. I have to get into the real world for + a while now. To be continued. + <antrik> gnu_srs: well, if you already know that the loop runs several + times before the error occurs, you apparently already looked at the + higher-level code that is relevant here... + <youpi> but it may be generic code, and not tell what calls it |