Messages in this thread | | | Date | Sun, 12 Nov 2006 15:45:53 -0800 | From | Andrew Morton <> | Subject | Re: 2.6.19-rc4-mm1: writev() _functional_ regression |
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On Sun, 12 Nov 2006 17:30:24 -0500 Nick Orlov <bugfixer@list.ru> wrote:
> Andrew, > > Somewhere in between 2.6.18-mm3 and 2.6.19-rc4-mm1 writev() got screwed. > It does not accept zero-length segments anymore. > > Bad thing that it is extremely easy to trigger (even w/o explicit writev calls). > For example the following innocent program will fail with 2.6.19-rc4-mm1: > > ====================== > #include <string.h> > #include <fstream> > > int main() > { > char buf[1024]; > memset(buf, 'A', sizeof(buf)); > std::ofstream ofs("test"); > //ofs << 1 << '\n'; > ofs.write(buf, sizeof(buf)); > return 0; > } > ====================== > > > Here is the corresponding part if strace: > > ====================== > open("test", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3 > writev(3, [{NULL, 0}, {"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 1024}], 2) = -1 EFAULT (Bad address) > close(3) = 0 > ====================== > > > With 2.6.18-mm3 it works > > ====================== > open("test", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3 > writev(3, [{NULL, 0}, {"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 1024}], 2) = 1024 > close(3) = 0 > ====================== > > > It works with 2.6.19-rc4-mm1 _if_ zero-length segments are eliminated > (by uncommenting ofs << 1 << '\n'): > > ====================== > open("test", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3 > writev(3, [{"1\n", 2}, {"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 1024}], 2) = 1026 > close(3) = 0 > ====================== > > > Given that _all_ applications using C++ streams are potentially affected > I think it's better to preserve the previous behavior even if it is > something from "undefined behavior world" (or a plain bug). > > The bug is quite dangerous (I was really close to wipe out my mp3 collection). >
OK, thanks. Those patches do need more work. I'll shelve them for a while. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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