From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932506AbcHOPIC (ORCPT ); Mon, 15 Aug 2016 11:08:02 -0400 Received: from mailapp01.imgtec.com ([195.59.15.196]:63139 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932469AbcHOPH7 (ORCPT ); Mon, 15 Aug 2016 11:07:59 -0400 Date: Mon, 15 Aug 2016 16:07:46 +0100 From: Eric Engestrom To: Jani Nikula , Tom St Denis , , Eric Engestrom , Michel =?utf-8?Q?D=C3=A4nzer?= , , , Xinliang Liu , David Zhang , Wei Yongjun , Vitaly Prosyak , Daniel Vetter , Junwei Zhang , Alex Deucher , Flora Cui , Gustavo Padovan , Christian =?utf-8?B?S8O2bmln?= Subject: Re: [PATCH] drm: make drm_get_format_name thread-safe Message-ID: <20160815150746.GF10429@imgtec.com> References: <20160815000247.20063-1-eric@engestrom.ch> <87eg5quzly.fsf@intel.com> <20160815125928.GC10429@imgtec.com> <87y43ytbsd.fsf@intel.com> <20160815135207.GG6232@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline In-Reply-To: <20160815135207.GG6232@phenom.ffwll.local> User-Agent: Mutt/1.6.2 (2016-07-01) X-Originating-IP: [10.60.4.28] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 15, 2016 at 03:52:07PM +0200, Daniel Vetter wrote: > On Mon, Aug 15, 2016 at 04:13:54PM +0300, Jani Nikula wrote: > > On Mon, 15 Aug 2016, Eric Engestrom wrote: > > > On Mon, Aug 15, 2016 at 12:54:01PM +0300, Jani Nikula wrote: > > >> On Mon, 15 Aug 2016, Eric Engestrom wrote: > > >> > Signed-off-by: Eric Engestrom > > >> > --- > > >> > > > >> > I moved the main bits to be the first diffs, shouldn't affect anything > > >> > when applying the patch, but I wanted to ask: > > >> > I don't like the hard-coded `32` the appears in both kmalloc() and > > >> > snprintf(), what do you think? If you don't like it either, what would > > >> > you suggest? Should I #define it? > > >> > > > >> > Second question is about the patch mail itself: should I send this kind > > >> > of patch separated by module, with a note requesting them to be squashed > > >> > when applying? It has to land as a single patch, but for review it might > > >> > be easier if people only see the bits they each care about, as well as > > >> > to collect ack's/r-b's. > > >> > > > >> > Cheers, > > >> > Eric > > >> > > > >> > --- > > >> > drivers/gpu/drm/amd/amdgpu/dce_v10_0.c | 6 ++-- > > >> > drivers/gpu/drm/amd/amdgpu/dce_v11_0.c | 6 ++-- > > >> > drivers/gpu/drm/amd/amdgpu/dce_v8_0.c | 6 ++-- > > >> > drivers/gpu/drm/drm_atomic.c | 5 ++-- > > >> > drivers/gpu/drm/drm_crtc.c | 21 ++++++++----- > > >> > drivers/gpu/drm/drm_fourcc.c | 17 ++++++----- > > >> > drivers/gpu/drm/hisilicon/kirin/kirin_drm_ade.c | 6 ++-- > > >> > drivers/gpu/drm/i915/i915_debugfs.c | 11 ++++++- > > >> > drivers/gpu/drm/i915/intel_atomic_plane.c | 6 ++-- > > >> > drivers/gpu/drm/i915/intel_display.c | 39 ++++++++++++++++--------- > > >> > drivers/gpu/drm/radeon/atombios_crtc.c | 12 +++++--- > > >> > include/drm/drm_fourcc.h | 2 +- > > >> > 12 files changed, 89 insertions(+), 48 deletions(-) > > >> > > > >> > diff --git a/drivers/gpu/drm/drm_fourcc.c b/drivers/gpu/drm/drm_fourcc.c > > >> > index 0645c85..38216a1 100644 > > >> > --- a/drivers/gpu/drm/drm_fourcc.c > > >> > +++ b/drivers/gpu/drm/drm_fourcc.c > > >> > @@ -39,16 +39,14 @@ static char printable_char(int c) > > >> > * drm_get_format_name - return a string for drm fourcc format > > >> > * @format: format to compute name of > > >> > * > > >> > - * Note that the buffer used by this function is globally shared and owned by > > >> > - * the function itself. > > >> > - * > > >> > - * FIXME: This isn't really multithreading safe. > > >> > + * Note that the buffer returned by this function is owned by the caller > > >> > + * and will need to be freed. > > >> > */ > > >> > const char *drm_get_format_name(uint32_t format) > > >> > > >> I find it surprising that a function that allocates a buffer returns a > > >> const pointer. Some userspace libraries have conventions about the > > >> ownership based on constness. > > >> > > >> (I also find it suprising that kfree() takes a const pointer; arguably > > >> that call changes the memory.) > > >> > > >> Is there precedent for this? > > >> > > >> BR, > > >> Jani. > > > > > > It's not a const pointer, it's a normal pointer to a const char, i.e. > > > you can do as you want with the pointer but you shouldn't change the > > > chars it points to. > > > > Ermh, that's what I meant even if I was sloppy in my reply. And arguably > > freeing the bytes the pointer points at changes them, albeit subtly. And > > having a function return a pointer to const data is often an indication > > that the ownership of the data isn't transfered, i.e. you're not > > supposed to free it yourself. > > I already applied the patch, but yes dropping the const would be a good > hint to callers that they now own that block of memory. Eric, can you pls > follow up with a fix up patch - drm-misc is non-rebasing? > -Daniel I didn't know about that convention. I'll send a fixup patch, but it'll have to wait until tomorrow night. I hope that's not an issue :( Cheers, Eric