From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <548838E5.8060701@nod.at> Date: Wed, 10 Dec 2014 13:13:25 +0100 From: Richard Weinberger MIME-Version: 1.0 References: <20141210104624.GB32280@tucsk.suse.de> <54882533.6080901@nod.at> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [BUG] uml panics with "Segfault with no mm" in v3.19-rc To: Geert Uytterhoeven Cc: Miklos Szeredi , Ley Foon Tan , Arnd Bergmann , "linux-kernel@vger.kernel.org" , Daniel Walter , user-mode-linux-devel List-ID: Am 10.12.2014 um 12:59 schrieb Geert Uytterhoeven: > On Wed, Dec 10, 2014 at 11:49 AM, Richard Weinberger wrote: >> Am 10.12.2014 um 11:46 schrieb Miklos Szeredi: >>> The guilty commit is: >>> >>> 00f634bc522d "asm-generic: add generic futex for !CONFIG_SMP" >> >> Thanks a lot Miklos! >> Your bisecting faster than I do. >> >> Let's dig into the issue! > > Do you need "select HAVE_FUTEX_CMPXCHG if FUTEX"? > Cfr. commit e571c58f313d35c5 ("m68k: Skip futex_atomic_cmpxchg_inatomic() > test") and commit 03b8c7b623c80af2 ("futex: Allow architectures to skip > futex_atomic_cmpxchg_inatomic() test"). Bingo! If UML selects HAVE_FUTEX_CMPXCHG the code path I've described in my previous mail is no longer taken and makes it work again. I did only a small test but nothing exploded so far. > BTW, I still think the real problem is the wrong address space, cfr. > "[PATCH/RFC] futex: Switch to USER_DS for futex test" > (http://www.spinics.net/lists/linux-m68k/msg06597.html), so you may also > want to try that. > However, that caused problems on s390, as it ran too early: > http://permalink.gmane.org/gmane.linux.kernel.next/30165 Yeah, this would also make sense for UML. Thanks, //richard