[4.9,14/41] arm64: Remove redundant mov from LL/SC cmpxchg

Message ID	20210305120851.988419372@linuxfoundation.org
State	New
Headers	show Return-Path: <stable-owner@kernel.org> From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, stable@vger.kernel.org, Will Deacon <will.deacon@arm.com>, Robin Murphy <robin.murphy@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Ben Hutchings <ben@decadent.org.uk> Subject: [PATCH 4.9 14/41] arm64: Remove redundant mov from LL/SC cmpxchg Date: Fri, 5 Mar 2021 13:22:21 +0100 Message-Id: <20210305120851.988419372@linuxfoundation.org> In-Reply-To: <20210305120851.255002428@linuxfoundation.org> References: <20210305120851.255002428@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	None \| expand [4.9,02/41] futex: Cleanup refcounting [4.9,03/41] futex: Pull rt_mutex_futex_unlock() out from under hb->lock [4.9,04/41] futex: Futex_unlock_pi() determinism [4.9,05/41] futex: Fix pi_state->owner serialization [4.9,06/41] futex: Fix more put_pi_state() vs. exit_pi_state_list() races [4.9,07/41] futex: Dont enable IRQs unconditionally in put_pi_state() [4.9,08/41] net: usb: qmi_wwan: support ZTE P685M modem [4.9,09/41] arm: kprobes: Allow to handle reentered kprobe on single-stepping [4.9,10/41] scripts: use pkg-config to locate libcrypto [4.9,11/41] scripts: set proper OpenSSL include dir also for sign-file [4.9,12/41] hugetlb: fix update_and_free_page contig page struct assumption [4.9,13/41] printk: fix deadlock when kernel panic [4.9,14/41] arm64: Remove redundant mov from LL/SC cmpxchg [4.9,15/41] arm64: Avoid redundant type conversions in xchg() and cmpxchg() [4.9,16/41] arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint [4.9,17/41] arm64: Use correct ll/sc atomic constraints [4.9,18/41] JFS: more checks for invalid superblock [4.9,19/41] xfs: Fix assert failure in xfs_setattr_size() [4.9,20/41] smackfs: restrict bytes count in smackfs write functions [4.9,21/41] net: fix up truesize of cloned skb in skb_prepare_for_shift() [4.9,22/41] mm/hugetlb.c: fix unnecessary address expansion of pmd sharing [4.9,23/41] staging: fwserial: Fix error handling in fwserial_create [4.9,24/41] x86/reboot: Add Zotac ZBOX CI327 nano PCI reboot quirk [4.9,25/41] vt/consolemap: do font sum unsigned [4.9,26/41] wlcore: Fix command execute failure 19 for wl12xx [4.9,27/41] pktgen: fix misuse of BUG_ON() in pktgen_thread_worker() [4.9,28/41] ath10k: fix wmi mgmt tx queue full due to race condition [4.9,29/41] x86/build: Treat R_386_PLT32 relocation as R_386_PC32 [4.9,30/41] Bluetooth: Fix null pointer dereference in amp_read_loc_assoc_final_data [4.9,31/41] staging: most: sound: add sanity check for function argument [4.9,32/41] media: uvcvideo: Allow entities with no pads [4.9,33/41] scsi: iscsi: Restrict sessions and handles to admin capabilities [4.9,34/41] sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output [4.9,35/41] scsi: iscsi: Ensure sysfs attributes are limited to PAGE_SIZE [4.9,36/41] scsi: iscsi: Verify lengths on passthrough PDUs [4.9,37/41] Xen/gnttab: handle p2m update errors on a per-slot basis [4.9,38/41] xen-netback: respect gnttab_map_refs()s return value [4.9,39/41] zsmalloc: account the number of compacted pages correctly [4.9,40/41] swap: fix swapfile read/write offset [4.9,41/41] media: v4l: ioctl: Fix memory leak in video_usercopy

Message ID

20210305120851.988419372@linuxfoundation.org

State

New

Headers

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Ben Hutchings <ben@decadent.org.uk>
Subject: [PATCH 4.9 14/41] arm64: Remove redundant mov from LL/SC cmpxchg
Date: Fri,  5 Mar 2021 13:22:21 +0100
Message-Id: <20210305120851.988419372@linuxfoundation.org>
In-Reply-To: <20210305120851.255002428@linuxfoundation.org>
References: <20210305120851.255002428@linuxfoundation.org>
User-Agent: quilt/0.66
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

Series

None | expand

Commit Message

Greg Kroah-Hartman March 5, 2021, 12:22 p.m. UTC

From: Robin Murphy <robin.murphy@arm.com>

commit 8df728e1ae614f592961e51f65d3e3212ede5a75 upstream.

The cmpxchg implementation introduced by commit c342f78217e8 ("arm64:
cmpxchg: patch in lse instructions when supported by the CPU") performs
an apparently redundant register move of [old] to [oldval] in the
success case - it always uses the same register width as [oldval] was
originally loaded with, and is only executed when [old] and [oldval] are
known to be equal anyway.

The only effect it seemingly does have is to take up a surprising amount
of space in the kernel text, as removing it reveals:

   text	   data	    bss	    dec	    hex	filename
12426658	1348614	4499749	18275021	116dacd	vmlinux.o.new
12429238	1348614	4499749	18277601	116e4e1	vmlinux.o.old

Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/arm64/include/asm/atomic_ll_sc.h |    1 -
 1 file changed, 1 deletion(-)

--- a/arch/arm64/include/asm/atomic_ll_sc.h
+++ b/arch/arm64/include/asm/atomic_ll_sc.h
@@ -264,7 +264,6 @@  __LL_SC_PREFIX(__cmpxchg_case_##name(vol
 	"	st" #rel "xr" #sz "\t%w[tmp], %" #w "[new], %[v]\n"	\
 	"	cbnz	%w[tmp], 1b\n"					\
 	"	" #mb "\n"						\
-	"	mov	%" #w "[oldval], %" #w "[old]\n"		\
 	"2:"								\
 	: [tmp] "=&r" (tmp), [oldval] "=&r" (oldval),			\
 	  [v] "+Q" (*(unsigned long *)ptr)				\

[4.9,14/41] arm64: Remove redundant mov from LL/SC cmpxchg

Commit Message

Patch