On Tue, Dec 16, 2025 at 2:38 PM Finn Thain <[email protected]> wrote: > > Some recent commits incorrectly assumed 4-byte alignment of locks. > That assumption fails on Linux/m68k (and, interestingly, would have > failed on Linux/cris also). The jump label implementation makes a > similar alignment assumption. > > The expectation that atomic_t and atomic64_t variables will be naturally > aligned seems reasonable, as indeed they are on 64-bit architectures. > But atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2, > openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned > on m68k. > > This patch brings a little uniformity by specifying natural alignment > for atomic types. One benefit is that atomic64_t variables do not get > split across a page boundary. The cost is that some structs grow which > leads to cache misses and wasted memory. > > Cc: Guo Ren <[email protected]> > Cc: [email protected] > Cc: Geert Uytterhoeven <[email protected]> > Cc: [email protected] > Cc: Dinh Nguyen <[email protected]> > Cc: Jonas Bonn <[email protected]> > Cc: Stefan Kristiansson <[email protected]> > Cc: Stafford Horne <[email protected]> > Cc: [email protected] > Cc: Yoshinori Sato <[email protected]> > Cc: Rich Felker <[email protected]> > Cc: John Paul Adrian Glaubitz <[email protected]> > Cc: [email protected] > Link: > https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7...@mail.gmail.com > Link: > https://lore.kernel.org/lkml/camuhmdw7ab13ddgs2acmqcix5objk0o2dg_fxzr8_g58rc1...@mail.gmail.com/ > Signed-off-by: Finn Thain <[email protected]> > --- > Changed since v2: > - Specify natural alignment for atomic64_t. > Changed since v1: > - atomic64_t now gets an __aligned attribute too. > - The 'Fixes' tag has been dropped because Lance sent a different fix > for commit e711faaafbe5 ("hung_task: replace blocker_mutex with encoded > blocker") that's suitable for -stable. > --- > include/asm-generic/atomic64.h | 2 +- > include/linux/types.h | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h > index 100d24b02e52..f22ccfc0df98 100644 > --- a/include/asm-generic/atomic64.h > +++ b/include/asm-generic/atomic64.h > @@ -10,7 +10,7 @@ > #include <linux/types.h> > > typedef struct { > - s64 counter; > + s64 __aligned(sizeof(s64)) counter; This alignment is okay for all.
Acked-by: Guo Ren <[email protected]> > } atomic64_t; > > #define ATOMIC64_INIT(i) { (i) } > diff --git a/include/linux/types.h b/include/linux/types.h > index 6dfdb8e8e4c3..a225a518c2c3 100644 > --- a/include/linux/types.h > +++ b/include/linux/types.h > @@ -179,7 +179,7 @@ typedef phys_addr_t resource_size_t; > typedef unsigned long irq_hw_number_t; > > typedef struct { > - int counter; > + int __aligned(sizeof(int)) counter; > } atomic_t; > > #define ATOMIC_INIT(i) { (i) } > -- > 2.49.1 > -- Best Regards Guo Ren
