| Message ID | 1409048930-21598-2-git-send-email-punit.agrawal@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Aug 26, 2014 at 11:28:45AM +0100, Punit Agrawal wrote: > According to the ARM ARMv7, explicit barriers are necessary when using > synchronisation primitives such as SWP{B}. The use of these > instructions does not automatically imply a barrier and any ordering > requirements by the software must be explicitly expressed with the use > of suitable barriers. > > Based on this, remove the barriers from SWP{B} emulation. > > Cc: Russell King <linux@arm.linux.org.uk> > Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> > --- > arch/arm/kernel/swp_emulate.c | 15 --------------- > 1 file changed, 15 deletions(-) Acked-by: Will Deacon <will.deacon@arm.com> Will
On Tue, Aug 26, 2014 at 11:28:45AM +0100, Punit Agrawal wrote: > According to the ARM ARMv7, explicit barriers are necessary when using > synchronisation primitives such as SWP{B}. The use of these > instructions does not automatically imply a barrier and any ordering > requirements by the software must be explicitly expressed with the use > of suitable barriers. > > Based on this, remove the barriers from SWP{B} emulation. > > Cc: Russell King <linux@arm.linux.org.uk> > Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> This patch is independent to the SWP emulation for arm64 series. Unless Russell has any objections, you should send it to his patch system (git send-email to patches@arm.linux.org.uk with "KernelVersion: v3..." after the commit log; I hope Russell drops the KernelVersion requirement some day ;)).
Catalin Marinas <catalin.marinas@arm.com> writes: > On Tue, Aug 26, 2014 at 11:28:45AM +0100, Punit Agrawal wrote: >> According to the ARM ARMv7, explicit barriers are necessary when using >> synchronisation primitives such as SWP{B}. The use of these >> instructions does not automatically imply a barrier and any ordering >> requirements by the software must be explicitly expressed with the use >> of suitable barriers. >> >> Based on this, remove the barriers from SWP{B} emulation. >> >> Cc: Russell King <linux@arm.linux.org.uk> >> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> > > This patch is independent to the SWP emulation for arm64 series. Unless > Russell has any objections, you should send it to his patch system (git > send-email to patches@arm.linux.org.uk with "KernelVersion: v3..." after > the commit log; I hope Russell drops the KernelVersion requirement some > day ;)). OK. Unless I hear any objections, I'll send the patch to Russell's system tomorrow.
diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c index b1b8988..74117b5 100644 --- a/arch/arm/kernel/swp_emulate.c +++ b/arch/arm/kernel/swp_emulate.c @@ -141,14 +141,6 @@ static int emulate_swpX(unsigned int address, unsigned int *data, while (1) { unsigned long temp; - /* - * Barrier required between accessing protected resource and - * releasing a lock for it. Legacy code might not have done - * this, and we cannot determine that this is not the case - * being emulated, so insert always. - */ - smp_mb(); - if (type == TYPE_SWPB) __user_swpb_asm(*data, address, res, temp); else @@ -161,13 +153,6 @@ static int emulate_swpX(unsigned int address, unsigned int *data, } if (res == 0) { - /* - * Barrier also required between acquiring a lock for a - * protected resource and accessing the resource. Inserted for - * same reason as above. - */ - smp_mb(); - if (type == TYPE_SWPB) swpbcounter++; else
According to the ARM ARMv7, explicit barriers are necessary when using synchronisation primitives such as SWP{B}. The use of these instructions does not automatically imply a barrier and any ordering requirements by the software must be explicitly expressed with the use of suitable barriers. Based on this, remove the barriers from SWP{B} emulation. Cc: Russell King <linux@arm.linux.org.uk> Signed-off-by: Punit Agrawal <punit.agrawal@arm.com> --- arch/arm/kernel/swp_emulate.c | 15 --------------- 1 file changed, 15 deletions(-)