On Sun, 2014-07-13 at 09:15 -0400, Peter Hurley wrote: > > I'm not sure I understand your point here, Ben. > > Suppose that two different spinlocks are used independently to > protect r-m-w access to adjacent data. In Oleg's example, > suppose spinlock 1 is used for access to the bitfield and > spinlock 2 is used for access to freeze_stop. > > What would prevent an accidental write to freeze_stop from the > kt_1 thread?
My point was to be weary of bitfields in general because access to them is always R-M-W, never atomic and that seem to escape people regularily :-) (Among other problems such as endian etc...) As for Oleg's example, it *should* have worked because the bitfield and the adjacent freeze_stop should have been accessed using load/stores that don't actually overlap, but the compiler bug causes the bitfield access to not properly use the basic type of the bitfield, but escalate to a full 64-bit R-M-W instead, thus incorrectly R-M-W'ing the field next door. Cheers, Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
