From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <55315058.6090502@siemens.com> Date: Fri, 17 Apr 2015 20:26:32 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <55314426.7040300@siemens.com> <20150417175028.GP1589@hermes.click-hack.org> <55314B85.2030708@siemens.com> <20150417180819.GQ1589@hermes.click-hack.org> <55314CA0.7070705@siemens.com> <20150417181254.GR1589@hermes.click-hack.org> <55314E36.3040201@siemens.com> <20150417182459.GS1589@hermes.click-hack.org> In-Reply-To: <20150417182459.GS1589@hermes.click-hack.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Dealing with too small thread stacks List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: Xenomai On 2015-04-17 20:24, Gilles Chanteperdrix wrote: > On Fri, Apr 17, 2015 at 08:17:26PM +0200, Jan Kiszka wrote: >> On 2015-04-17 20:12, Gilles Chanteperdrix wrote: >>> On Fri, Apr 17, 2015 at 08:10:40PM +0200, Jan Kiszka wrote: >>>> On 2015-04-17 20:08, Gilles Chanteperdrix wrote: >>>>> On Fri, Apr 17, 2015 at 08:05:57PM +0200, Jan Kiszka wrote: >>>>>> On 2015-04-17 19:50, Gilles Chanteperdrix wrote: >>>>>>> On Fri, Apr 17, 2015 at 07:34:30PM +0200, Jan Kiszka wrote: >>>>>>>> Hi, >>>>>>>> >>>>>>>> analyzing page faults of an application that prefers to set its own >>>>>>>> stacks, I noticed a problem in Xenomai (2 and 3), at least from the >>>>>>>> usability POV: We document the minimum stack stack as PTHREAD_STACK_MIN >>>>>>>> + 1 page, at least in Xenomai 3, and we enforce that on thread creation. >>>>>>>> However, enforcement is doomed to fail if the stack is preallocated (and >>>>>>>> that too small). >>>>>>>> >>>>>>>> As we cannot detect if the user set a stack address in pthread_attr_t, I >>>>>>>> would suggest to fail thread creation instead of performing it with >>>>>>>> improper parameters. Other suggestions? If not, I would prepare a patch >>>>>>>> for Xenomai 3 (for 2 only if desired). >>>>>>> >>>>>>> It seems to me we can detect the parameters in the pthread_attr_t >>>>>>> using pthread_attr_getstack. So, we can get __wrap_pthread_create to >>>>>>> fail if the size is not sufficient. >>>>>> >>>>>> Nope, unfortunately not: >>>>>> >>>>>> "If the pthread_attr_getstack() function is called before the stackaddr >>>>>> attribute has been set, the behavior is unspecified." >>>>> >>>>> It is unspecified by POSIX, but Xenomai supports only two >>>>> implementations, glibc and uClibc, so, we can look at what these two >>>>> libraries do. I would bet they return you a NULL stack pointer or >>>>> something. >>>> >>>> I would have expected that, too, but the results for glibc seem random. >>>> Plus there is the risk that something changes, thus we become >>>> version-dependent. >>> >>> Ok then, what about the influence of pthread_attr_setstack() on >>> pthread_attr_getstacksize(), maybe more luck there? >> >> setstack defines the size getstacksize returns. So does setstacksize. >> >> What happens during setstacksize is apparently that the address is set >> to NULL - size. But, again, that is just the current glibc behaviour. > > Yes, ok, but in order to test the stack size passed by the user, it > simply means we can use getstacksize and bail out if not sufficient. Sure, that would be the best way. Along that, I would recommend raising the minimum to 2*PTHREAD_STACK_MIN. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux