On 2010-02-20, at 17:13, Nathan Whitehorn wrote: > Author: nwhitehorn > Date: Sat Feb 20 16:13:43 2010 > New Revision: 204126 > URL: http://svn.freebsd.org/changeset/base/204126 > > Log: > Merge r198724 to Book-E. casuword() non-atomically read the current value > of its argument before atomically replacing it, which could occasionally > return the wrong value on an SMP system. This resulted in user mutex > operations hanging when using threaded applications.
Have you got a particular test case when this was breaking, so I can test? > Modified: > head/sys/powerpc/booke/copyinout.c > > Modified: head/sys/powerpc/booke/copyinout.c > ============================================================================== > --- head/sys/powerpc/booke/copyinout.c Sat Feb 20 16:12:37 2010 > (r204125) > +++ head/sys/powerpc/booke/copyinout.c Sat Feb 20 16:13:43 2010 > (r204126) > @@ -295,8 +295,19 @@ casuword(volatile u_long *addr, u_long o > return (EFAULT); > } > > - val = *addr; > - (void) atomic_cmpset_32((volatile uint32_t *)addr, old, new); > + __asm __volatile ( > + "1:\tlwarx %0, 0, %2\n\t" /* load old value */ > + "cmplw %3, %0\n\t" /* compare */ > + "bne 2f\n\t" /* exit if not equal */ > + "stwcx. %4, 0, %2\n\t" /* attempt to store */ > + "bne- 1b\n\t" /* spin if failed */ > + "b 3f\n\t" /* we've succeeded */ > + "2:\n\t" > + "stwcx. %0, 0, %2\n\t" /* clear reservation (74xx) */ The 74xx comment reference is somewhat confusing as the clear reservation operation is pretty uniform accross 32-bit PowerPC I guess, and not 74xx specific. Rafal _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
