Date: Thu, 28 Dec 2017 17:25:25 +0100 From: Jilles Tjoelker <jilles@stack.nl> To: Antoine Brodin <antoine@freebsd.org> Cc: Mateusz Guzik <mjg@freebsd.org>, David Chisnall <theraven@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r325726 - head/sys/kern Message-ID: <20171228162525.GA32705@stack.nl> In-Reply-To: <CAALwa8nX_HwdayRmJkC3bBqZV6UmOUfpa29rpGhB8gT2%2Bp2XKQ@mail.gmail.com> References: <201711112239.vABMdXS2053880@repo.freebsd.org> <CAALwa8nX_HwdayRmJkC3bBqZV6UmOUfpa29rpGhB8gT2%2Bp2XKQ@mail.gmail.com>
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On Thu, Dec 28, 2017 at 12:40:31PM +0000, Antoine Brodin wrote: > On Sat, Nov 11, 2017 at 10:39 PM, Mateusz Guzik <mjg@freebsd.org> wrote: > > Author: mjg > > Date: Sat Nov 11 22:39:33 2017 > > New Revision: 325726 > > URL: https://svnweb.freebsd.org/changeset/base/325726 > > Log: > > Avoid locking and refing in sysctl_kern_proc_args if possible. > > Turns out the sysctl is called a lot e.g. by pkg-static. > > Modified: > > head/sys/kern/kern_proc.c > There is a regression after this commit: x11-toolkits/gnustep-gui no > longer builds. > You can find a failure log at > http://pb2.nyi.freebsd.org/data/111i386-default-PR224618/2017-12-28_12h28m51s/logs/errors/gnustep-gui-0.25.1_3.log > The failure seems to be from lang/gnustep-base: > /* get the argument vectors */ > vectors = kvm_getargv(kptr, proc_ptr, 0); It looks like the new fast path only works properly if p->p_args is not NULL. If p->p_args is NULL, this usually means that the arguments are longer than ps_arg_cache_limit and must be retrieved from (pageable) process memory and not wired p->p_args->ar_args. It is possible to duplicate that piece of code as well but that is probably not worth it. A simple reproducer is sh -c 'n=$(sysctl -n kern.ps_arg_cache_limit); exec ps -p "$$" -o "args=$(printf "%0${n}d" 0)"' On head, the second line is [ps] indicating that KERN_PROC_ARGS did not return the expected string. On stable/10 and stable/11, the second line is a truncated version of the command line like ps -p 86963 -o args=0000000000000000000000000000000000000000000000000000000000 A prerequisite for this reproducer is that kern.ps_arg_cache_limit is not set so high that it is impractical to exceed it but not {ARG_MAX}. -- Jilles Tjoelker
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