From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Michael Neuling To: Anshuman Khandual Subject: Re: [PATCH 0/3] Add new ptrace request macros on PowerPC In-reply-to: <535F997B.3000500@linux.vnet.ibm.com> References: <1396422144-11032-1-git-send-email-khandual@linux.vnet.ibm.com> <533BD922.4070009@linux.vnet.ibm.com> <535F4E10.2020300@linux.vnet.ibm.com> <535F5BDE.2030309@linux.vnet.ibm.com> <535F997B.3000500@linux.vnet.ibm.com> Date: Wed, 30 Apr 2014 10:29:05 +1000 Message-ID: <20730.1398817745@ale.ozlabs.ibm.com> Cc: Linux PPC dev , linux-kernel@vger.kernel.org, avagin@openvz.org, roland@redhat.com, oleg@redhat.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Anshuman Khandual wrote: > On 04/29/2014 01:52 PM, Michael Neuling wrote: > > That's not what that patch does. It shouldn't make any user visible changes > > to DSCR or PPR. > > It may not when it runs uninterrupted but after the tracee process has > stopped, thread.dscr reflects the default DSCR value as mentioned > before. This can be proved by changing the "dscr_default" value in > arch/powerpc/sysfs.c file. The intention with DSCR is that if the user changes the DSCR, the kernel should always save/restore it. If you are seeing something else, then that is a bug. Anton has a test case for this here: http://ozlabs.org/~anton/junkcode/dscr_explicit_test.c If that is failing, then there is a bug that we need to fix. The PPR is the same, except that the kernel can change it over a syscall. > > Over syscall PPR and DSCR may change. Sorry, this should be only PPR. DSCR shouldn't change over a syscall, at least that's the intention. > > Depending on your test case, that may > > be your problem. > > I would guess when the tracee process stops for ptrace analysis, tm_reclaim or > tm_recheckpoint path might be crossed which is causing this dscr_default value > to go into thread_struct. That shouldn't happen. If that's happening, it's a bug. Mikey