# git rev-parse -q --verify 66be4e66a7f422128748e3c3ef6ee72b20a6197b^{commit} 66be4e66a7f422128748e3c3ef6ee72b20a6197b already have revision, skipping fetch # git checkout -q -f -B kisskb 66be4e66a7f422128748e3c3ef6ee72b20a6197b # git clean -qxdf # < git log -1 # commit 66be4e66a7f422128748e3c3ef6ee72b20a6197b # Author: Linus Torvalds # Date: Mon Jun 3 13:26:20 2019 -0700 # # rcu: locking and unlocking need to always be at least barriers # # Herbert Xu pointed out that commit bb73c52bad36 ("rcu: Don't disable # preemption for Tiny and Tree RCU readers") was incorrect in making the # preempt_disable/enable() be conditional on CONFIG_PREEMPT_COUNT. # # If CONFIG_PREEMPT_COUNT isn't enabled, the preemption enable/disable is # a no-op, but still is a compiler barrier. # # And RCU locking still _needs_ that compiler barrier. # # It is simply fundamentally not true that RCU locking would be a complete # no-op: we still need to guarantee (for example) that things that can # trap and cause preemption cannot migrate into the RCU locked region. # # The way we do that is by making it a barrier. # # See for example commit 386afc91144b ("spinlocks and preemption points # need to be at least compiler barriers") from back in 2013 that had # similar issues with spinlocks that become no-ops on UP: they must still # constrain the compiler from moving other operations into the critical # region. # # Now, it is true that a lot of RCU operations already use READ_ONCE() and # WRITE_ONCE() (which in practice likely would never be re-ordered wrt # anything remotely interesting), but it is also true that that is not # globally the case, and that it's not even necessarily always possible # (ie bitfields etc). # # Reported-by: Herbert Xu # Fixes: bb73c52bad36 ("rcu: Don't disable preemption for Tiny and Tree RCU readers") # Cc: stable@kernel.org # Cc: Boqun Feng # Cc: Paul E. McKenney # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc --version # < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-ld --version # < git log --format=%s --max-count=1 66be4e66a7f422128748e3c3ef6ee72b20a6197b # < make -s -j 48 ARCH=arm O=/kisskb/build/linus_at91_dt_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi- at91_dt_defconfig # make -s -j 48 ARCH=arm O=/kisskb/build/linus_at91_dt_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi- /kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl': /kisskb/src/kernel/printk/printk.c:194:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/ipc/shm.c: In function 'ksys_shmdt': /kisskb/src/ipc/shm.c:1712:59: warning: 'file' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/core/gen_stats.c: In function '__gnet_stats_copy_basic': /kisskb/src/net/core/gen_stats.c:157:19: warning: 'seq' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/gpio/gpiolib-of.c: In function 'of_gpiochip_add': /kisskb/src/drivers/gpio/gpiolib-of.c:461:8: warning: 'dflags' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/gpio/gpiolib-of.c:447:19: note: 'dflags' was declared here /kisskb/src/drivers/gpio/gpiolib-of.c:461:8: warning: 'lflags' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/gpio/gpiolib-of.c:446:16: note: 'lflags' was declared here /kisskb/src/drivers/gpu/drm/drm_dp_mst_topology.c: In function 'drm_dp_sideband_msg_build': /kisskb/src/drivers/gpu/drm/drm_dp_mst_topology.c:423:23: warning: 'hdrlen' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/core/dev.c: In function 'validate_xmit_skb_list': /kisskb/src/net/core/dev.c:3415:15: warning: 'tail' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/lib/mpi/mpicoder.c: In function 'mpi_read_raw_from_sgl': /kisskb/src/lib/mpi/mpicoder.c:336:12: warning: 'buff' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/mm/vmalloc.c: In function 'alloc_vmap_area': /kisskb/src/mm/vmalloc.c:976:28: warning: 'lva' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/mm/vmalloc.c:916:20: note: 'lva' was declared here /kisskb/src/drivers/mtd/ubi/eba.c: In function 'try_write_vid_and_data': /kisskb/src/drivers/mtd/ubi/eba.c:988:7: warning: 'opnum' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/lib/rhashtable.c: In function 'rht_deferred_worker': /kisskb/src/include/linux/rhashtable.h:110:10: warning: 'next' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/lib/rhashtable.c:225:28: note: 'next' was declared here /kisskb/src/drivers/gpu/drm/drm_atomic.c: In function 'drm_atomic_check_only': /kisskb/src/drivers/gpu/drm/drm_atomic.c:420:38: warning: 'crtc_state' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/gpu/drm/drm_atomic.c:399:25: note: 'crtc_state' was declared here /kisskb/src/drivers/pwm/pwm-atmel-hlcdc.c: In function 'atmel_hlcdc_pwm_apply': /kisskb/src/drivers/pwm/pwm-atmel-hlcdc.c:78:56: warning: 'clk_period_ns' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/rtc/rtc-rv3029c2.c: In function 'rv3029_probe': /kisskb/src/drivers/rtc/rtc-rv3029c2.c:664:3: warning: 'elem' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/rtc/rtc-rv3029c2.c:643:40: note: 'elem' was declared here /kisskb/src/fs/proc/inode.c: In function 'proc_reg_open': /kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c:331:21: note: 'pdeo' was declared here /kisskb/src/net/mac80211/mlme.c: In function 'ieee80211_rx_mgmt_beacon': /kisskb/src/net/mac80211/mlme.c:1578:3: warning: 'pwr_level_cisco' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/mac80211/mlme.c:1535:6: note: 'pwr_level_cisco' was declared here /kisskb/src/net/ipv4/fib_semantics.c: In function 'fib_create_info': /kisskb/src/net/ipv4/fib_semantics.c:1023:12: warning: 'err' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/ipv4/fib_semantics.c:967:6: note: 'err' was declared here Completed OK # rm -rf /kisskb/build/linus_at91_dt_defconfig_arm # Build took: 0:00:51.755714