Date: Fri, 19 Sep 2014 15:27:25 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Konstantin Belousov <kostikbel@gmail.com>, "Ivan A. Kosarev" <ivan@ivan-labs.com> Subject: Re: libthr and main thread stack size Message-ID: <5242716.s4iaScq0Bu@ralph.baldwin.cx> In-Reply-To: <20140916081324.GQ2737@kib.kiev.ua> References: <53E36E84.4060806@ivan-labs.com> <FEB60EB5-546D-454D-AE62-B2483246E42C@scsiguy.com> <20140916081324.GQ2737@kib.kiev.ua>
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On Tuesday, September 16, 2014 11:13:24 AM Konstantin Belousov wrote: > On Mon, Sep 15, 2014 at 03:47:41PM -0600, Justin T. Gibbs wrote: > > On Aug 8, 2014, at 5:22 AM, Konstantin Belousov <kostikbel@gmail.com> > > wrote: > > > > ? > > > > > Below is the patch which adds environment variable > > > LIBPTHREAD_BIGSTACK_MAIN. Setting it to any value results in the > > > main thread stack left as is, and other threads allocate stack > > > below the area of RLIMIT_STACK. Try it. I do not want to set this > > > behaviour as default. > > > > Is there a reason this should not be the default? Looking at the > > getrlimit() page on the OpenGroup?s site they say: > > > > RLIMIT_STACK This is the maximum size of the initial thread's stack, > > in bytes. The implementation does not automatically grow the stack > > beyond this limit. If this limit is exceeded, SIGSEGV shall be > > generated for the thread. If the thread is blocking SIGSEGV, or the > > process is ignoring or catching SIGSEGV and has not made arrangements > > to use an alternate stack, the disposition of SIGSEGV shall be set to > > SIG_DFL before it is generated. > > > > Does posix say something different? > > > > I ran into this issue when debugging a segfault on Postgres when > > running an (arguably quite bogus) query that should have fit within > > both the configured stack rlimit and Postgres? configured stack limit. > > The Postgres backend is really just single threaded, but happens > > to pull in libpthread due to the threading support in some of the > > libraries it uses. The segfault definitely violates POLA. > > > > ? Justin > > I am conservative to not disturb the address space layout in single go. > If enough people test this setting, I can consider flipping the default > to the reverse. > > I am still curious why the things were done in this way, but nobody > replied. I suspect it was done out of reasons of being overly conservative in interpreting RLIMIT_STACK. I think it is quite surprising behavior though and would rather we make your option the default and implement what the Open Group says above. -- John Baldwin
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