Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Tue, 23 Aug 2016 15:45:51 +0200 | Subject | Re: [PATCH tip/core/rcu 2/2] documentation: Record reason for rcu_head two-byte alignment |
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Hi Paul,
On Tue, Aug 23, 2016 at 3:43 PM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > On Tue, Aug 23, 2016 at 08:39:18AM +0200, Geert Uytterhoeven wrote: >> On Mon, Aug 22, 2016 at 11:16 PM, Paul E. McKenney >> <paulmck@linux.vnet.ibm.com> wrote: >> > On Mon, Aug 22, 2016 at 10:48:57PM +0200, Geert Uytterhoeven wrote: >> >> On Mon, Aug 22, 2016 at 9:54 PM, Paul E. McKenney >> >> <paulmck@linux.vnet.ibm.com> wrote: >> >> > On Mon, Aug 22, 2016 at 03:18:54PM -0400, Steven Rostedt wrote: >> >> >> On Mon, 22 Aug 2016 20:56:09 +0200 >> >> >> Peter Zijlstra <peterz@infradead.org> wrote: >> >> >> >> >> >> > > Don't we have __alignof__(void *) to avoid #ifdef CONFIG_M68K and >> >> >> > > other new macros ? >> >> > >> >> > Hmmm... Does __alignof__(void *) give two-byte alignment on m68k, >> >> > allowing something like this? Heh!!! It is already there. ;-) >> >> > >> >> > struct callback_head { >> >> > struct callback_head *next; >> >> > void (*func)(struct callback_head *head); >> >> > } __attribute__((aligned(sizeof(void *)))); >> >> >> >> No, it's aligning to sizeof(void *) (4 on m68k), not __alignof__(void *). >> > >> > Right you are. Commit 720abae3d68ae from Kirill A. Shutemov in November >> > 2015. >> > >> > Given that you haven't complained, I am guessing that this works for you. >> > If so, I can make the __call_rcu() WARN_ON() more strict. >> > Again, does the current state work for you?
>> Yes it does. See also your commit 1146edcbef378922 ("rcu: Loosen __call_rcu()'s >> rcu_head alignment constraint"). > > Understood! > > But given that all architectures now provide at least four-byte alignment > for the rcu_head structure, isn't it now OK for me to tighten up __call_rcu()'s > check, for example, to this? > > WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
Yes, I agree with that.
Thanks!
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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