On Mon, Aug 22, 2016 at 10:48:57PM +0200, Geert Uytterhoeven wrote: > Hi Paul, > > On Mon, Aug 22, 2016 at 9:54 PM, Paul E. McKenney > <paul...@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 <pet...@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. > > #define rcu_head callback_head > > > > If so, that does sound quite attractive! Might need the WARN_ON() > > anyway, to flag wild pointers if nothing else. > > > > Adding Geert on CC for his thoughts. > > __alignof__(void *) is indeed 2 on m68k, and h8300. > > Note that it is 1 on crisv32! Gah... ((__alignof__(void *) + 1) & ~0x1), eh? > It's 4 or 8 on anything else I have a cross-compiler for. > > $ cat a.c > unsigned x = __alignof__(void *); > $ for i in /opt/cross/*/*/bin/*gcc; do echo +++ $i +++; $i -c -S a.c; > cat a.s; done | less Thank you for checking! Again, does the current state work for you? Thanx, Paul