Re: [patch 00/21] mutex subsystem, -V14

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




Anyway, here is some disassembly of some of the code generated with my comments:

c00000000049bf9c <.mutex_lock>:
c00000000049bf9c:       7c 00 06 ac     eieio
c00000000049bfa0:       7d 20 18 28     lwarx   r9,r0,r3
c00000000049bfa4:       31 29 ff ff     addic   r9,r9,-1


The eieio is completly unnecessary, it got picked up from atomic_dec_return (Anton, why is there an eieio at the start of atomic_dec_return in the first place?).


a mutex is like a spinlock, it must prevent loads and stores within the critical section from 'leaking outside the critical section' [they must not be reordered to before the mutex_lock(), nor to after the mutex_unlock()] - hence the barriers added by atomic_dec_return() are very much needed.

The bne- and isync together form a sufficient import barrier. See PowerPC Book2 Appendix B.2.1.1

And if the eieio was necessary it should come after not before twidling the lock bits.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[Index of Archives]     [Kernel Newbies]     [Netfilter]     [Bugtraq]     [Photo]     [Stuff]     [Gimp]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Video 4 Linux]     [Linux for the blind]     [Linux Resources]
  Powered by Linux