Hi Alexey,
On Mon, Jul 9, 2018 at 10:37 AM Alexey Brodkin Alexey.Brodkin@synopsys.com wrote:
On Mon, 2018-07-09 at 09:52 +0200, Geert Uytterhoeven wrote:
On Mon, Jul 9, 2018 at 9:22 AM Alexey Brodkin Alexey.Brodkin@synopsys.com wrote:
On Mon, 2018-07-09 at 09:07 +0200, Geert Uytterhoeven wrote:
On Mon, Jul 9, 2018 at 7:49 AM Greg KH greg@kroah.com wrote:
On Mon, Jul 09, 2018 at 07:44:44AM +0300, Alexey Brodkin wrote:
Depending on ABI "long long" type of a particular 32-bit CPU might be aligned by either word (32-bits) or double word (64-bits).
Or even 16-bit (on e.g. m68k).
Indeed, thanks for the note! Will add this in my v3.
Note that in this particular case, the field will probably always be aligned to 4 bytes, as the struct will be allocated using *alloc().
Well I think maybe it worth mentioning only 32-bit and 64-bit alignments in this particular case because as it was mentioned initially in the comment there're 3 pointers before "data" field and for 32-bit machines I guess we may safely assume that a pointer size is 32-bit.
This leaves us only one problematic situation 32-bit instead of 64-bit alignment.
For ARC I'd like this fix to be back-ported starting from v4.8 where we added support of "native" atomic64_t, see commit ce6365270ecd (" ARCv2: Implement atomic64 based on LLOCKD/SCONDD instructions").
What about m68k, do you have any preference of earliest kernel version where this fix might be useful?
Given m68k is 32-bit, it will access atomic64_t variables while holding a spinlock, so it should still be safe without this change.
Well ARC and ARMv7 are 32-bit machines as well still both have a special instructions to read/write 64-bit data.
Sure.
Not to mention no one will try etnaviv on m68k ;-)
See it was just a trigger case but other GPUs that use or will use DRM GPU scheduler are good candidates to it that problem and not to mention some other users of atomic64_t.
But from you above comment I may deduce that m68k doesn't have instructions for 64-bit data; in that case there's no reason to worry at least about struct devres_node :)
That's correct: m68k has no instructions for 64-bit data.
Gr{oetje,eeting}s,
Geert