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The use of ACCESS_ONCE() looks like a micro-optimization to force gcc to use an indexed load for the register address, but it has an absolutely detrimental effect on builds with gcc-5 and CONFIG_KASAN=y, leading to a very likely kernel stack overflow aside from very complex object code: hisilicon/hns/hns_dsaf_gmac.c: In function 'hns_gmac_update_stats': hisilicon/hns/hns_dsaf_gmac.c:419:1: error: the frame size of 2912 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_ppe.c: In function 'hns_ppe_reset_common': hisilicon/hns/hns_dsaf_ppe.c:390:1: error: the frame size of 1184 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_ppe.c: In function 'hns_ppe_get_regs': hisilicon/hns/hns_dsaf_ppe.c:621:1: error: the frame size of 3632 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_rcb.c: In function 'hns_rcb_get_common_regs': hisilicon/hns/hns_dsaf_rcb.c:970:1: error: the frame size of 2784 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_gmac.c: In function 'hns_gmac_get_regs': hisilicon/hns/hns_dsaf_gmac.c:641:1: error: the frame size of 5728 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_rcb.c: In function 'hns_rcb_get_ring_regs': hisilicon/hns/hns_dsaf_rcb.c:1021:1: error: the frame size of 2208 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_main.c: In function 'hns_dsaf_comm_init': hisilicon/hns/hns_dsaf_main.c:1209:1: error: the frame size of 1904 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_xgmac.c: In function 'hns_xgmac_get_regs': hisilicon/hns/hns_dsaf_xgmac.c:748:1: error: the frame size of 4704 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_main.c: In function 'hns_dsaf_update_stats': hisilicon/hns/hns_dsaf_main.c:2420:1: error: the frame size of 1088 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] hisilicon/hns/hns_dsaf_main.c: In function 'hns_dsaf_get_regs': hisilicon/hns/hns_dsaf_main.c:2753:1: error: the frame size of 10768 bytes is larger than 1024 bytes [-Werror=frame-larger-than=] This does not seem to happen any more with gcc-7, but removing the ACCESS_ONCE seems safe anyway and it avoids a serious issue for some people. I have verified that with gcc-5.3.1, the object code we get is better in the new version both with and without CONFIG_KASAN, as we no longer allocate a 1344 byte stack frame for hns_dsaf_get_regs() but otherwise have practically identical object code. With gcc-7.0.0, removing ACCESS_ONCE has no effect, the object code is already good either way. This patch is probably not urgent to get into 4.11 as only KASAN=y builds with certain compilers are affected, but I still think it makes sense to backport into older kernels. Cc: stable@vger.kernel.org Fixes: 511e6bc ("net: add Hisilicon Network Subsystem DSAF support") Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.