Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 22 Sep 2016 15:23:59 -0700 | Subject | Re: [RFC PATCH 2/8] thread_info: allow custom in-task thread_info |
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On Sep 21, 2016 12:28 AM, "Mark Rutland" <mark.rutland@arm.com> wrote: > > Hi Andy, > > On Fri, Sep 16, 2016 at 08:11:14AM -0700, Andy Lutomirski wrote: > > > On Thu, Sep 15, 2016 at 11:37:47AM -0700, Andy Lutomirski wrote: > > > Just to check, what do you mean to happen with the flags field? Should > > > that always be in the generic thread_info? e.g. > > > > > > struct thread_info { > > > u32 flags; > > > #ifdef arch_thread_info > > > struct arch_thread_info arch_ti; > > > #endif > > > }; > > > > Exactly. Possibly with a comment that using thread_struct should be > > preferred and that arch_thread_info should be used only if some header > > file requires access via current_thread_info() or task_thread_info(). > > While fixing up these patches, I realised that I'm somewhat concerned by > flags becoming a u32 (where it was previously an unsigned long for > arm64). > > The generic {test,set,*}_ti_thread_flag() helpers use the usual bitops, > which perform accesses of sizeof(unsigned long) at a time, and for arm64 > these need to be naturally-aligned. > > We happen to get that alignment from subsequent fields in task_struct > and/or thread_info, and for arm64 we don't seem to have a problem with > tearing, but it feels somewhat fragile, and leaves me uneasy. > > Looking at the git log, it seems that x86 also use unsigned long until > commit affa219b60a11b32 ("x86: change thread_info's flag field back to > 32 bits"), where if I'm reading correctly, this was done to get rid of > unnecessary padding. With THREAD_INFO_IN_STACK, thread_info::flags is > immediately followed by a long on x86, so we save no padding. > > Given all that, can we make the generic thread_info::flags an unsigned > long, matching what the thread flag helpers implicitly assume? >
Yes. Want to send the patch or should I?
--Andy
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