xavi/android_kernel_m2note/arch/arc/include/asm/cmpxchg.h, branch ng-7.1.2Unnamed repository; edit this file 'description' to name the repository.
https://gitea.privatedns.org/xavi/android_kernel_m2note/atom?h=ng-7.1.22016-08-26T17:29:34+00:00ARC: add compiler barrier to LLSC based cmpxchg2016-08-26T17:29:34+00:00Vineet Guptavgupta@synopsys.com2014-11-13T10:24:01+00:00urn:sha1:340a293baa281b0130dc3642b448c4ff0150289b
commit d57f727264f1425a94689bafc7e99e502cb135b5 upstream.
When auditing cmpxchg call sites, Chuck noted that gcc was optimizing
away some of the desired LDs.
| do {
| new = old = *ipi_data_ptr;
| new |= 1U << msg;
| } while (cmpxchg(ipi_data_ptr, old, new) != old);
was generating to below
| 8015cef8: ld r2,[r4,0] <-- First LD
| 8015cefc: bset r1,r2,r1
|
| 8015cf00: llock r3,[r4] <-- atomic op
| 8015cf04: brne r3,r2,8015cf10
| 8015cf08: scond r1,[r4]
| 8015cf0c: bnz 8015cf00
|
| 8015cf10: brne r3,r2,8015cf00 <-- Branch doesn't go to orig LD
Although this was fixed by adding a ACCESS_ONCE in this call site, it
seems safer (for now at least) to add compiler barrier to LLSC based
cmpxchg
Reported-by: Chuck Jordan <cjordan@synopsys.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Guendhoer <stefan@guendhoer.com>
first commit2016-08-15T02:19:42+00:00Meizu OpenSourcepatchwork@meizu.com2016-08-15T02:19:42+00:00urn:sha1:d2e1446d81725c351dc73a03b397ce043fb18452