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06646da014
linux/kernel
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Paul E. McKenney 06646da014 bpf: Fold smp_mb__before_atomic() into atomic_set_release() 
The bpf_user_ringbuf_drain() BPF_CALL function uses an atomic_set()
immediately preceded by smp_mb__before_atomic() so as to order storing
of ring-buffer consumer and producer positions prior to the atomic_set()
call's clearing of the ->busy flag, as follows:

        smp_mb__before_atomic();
        atomic_set(&rb->busy, 0);

Although this works given current architectures and implementations, and
given that this only needs to order prior writes against a later write.
However, it does so by accident because the smp_mb__before_atomic()
is only guaranteed to work with read-modify-write atomic operations, and
not at all with things like atomic_set() and atomic_read().

Note especially that smp_mb__before_atomic() will not, repeat *not*,
order the prior write to "a" before the subsequent non-read-modify-write
atomic read from "b", even on strongly ordered systems such as x86:

        WRITE_ONCE(a, 1);
        smp_mb__before_atomic();
        r1 = atomic_read(&b);

Therefore, replace the smp_mb__before_atomic() and atomic_set() with
atomic_set_release() as follows:

        atomic_set_release(&rb->busy, 0);

This is no slower (and sometimes is faster) than the original, and also
provides a formal guarantee of ordering that the original lacks.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/ec86d38e-cfb4-44aa-8fdb-6c925922d93c@paulmck-laptop
2023-10-24 14:26:07 +02:00
..
bpf bpf: Fold smp_mb__before_atomic() into atomic_set_release() 2023-10-24 14:26:07 +02:00
cgroup cgroup: Prepare for using css_task_iter_*() in BPF 2023-10-19 17:02:46 -07:00
configs Kbuild updates for v6.6 2023-09-05 11:01:47 -07:00
debug printk changes for 6.6 2023-09-04 13:20:19 -07:00
dma swiotlb: fix the check whether a device has used software IO TLB 2023-09-27 11:19:15 +02:00
entry entry: Remove empty addr_limit_user_check() 2023-08-23 10:32:39 +02:00
events powerpc updates for 6.6 2023-08-31 12:43:10 -07:00
futex mm/mm_init.c: remove obsolete macro HASH_SMALL 2023-08-18 10:12:07 -07:00
gcov gcov: shut up missing prototype warnings for internal stubs 2023-08-18 10:18:58 -07:00
irq Boring updates for the interrupt subsystem: 2023-08-28 14:33:11 -07:00
kcsan kcsan: Don't expect 64 bits atomic builtins from 32 bits architectures 2023-06-09 23:29:50 +10:00
livepatch livepatch: Make 'klp_stack_entries' static 2023-06-05 13:56:52 +02:00
locking - An extensive rework of kexec and crash Kconfig from Eric DeVolder 2023-08-29 14:53:51 -07:00
module module/decompress: use vmalloc() for zstd decompression workspace 2023-08-29 09:39:08 -07:00
power PM: hibernate: Fix copying the zero bitmap to safe pages 2023-10-04 20:43:44 +02:00
printk Merge branch 'rework/misc-cleanups' into for-linus 2023-10-11 12:58:14 +02:00
rcu TTY/Serial driver changes for 6.6-rc1 2023-09-01 09:38:00 -07:00
sched cpufreq: schedutil: Update next_freq when cpufreq_limits change 2023-10-05 22:09:50 +02:00
time posix-clock: introduce posix_clock_context concept 2023-10-15 20:07:52 +01:00
trace bpf-next-for-netdev 2023-10-16 21:05:33 -07:00
.gitignore
acct.c audit/stable-6.6 PR 20230829 2023-08-30 08:17:35 -07:00
async.c
audit_fsnotify.c
audit_tree.c
audit_watch.c
audit.c audit: move trailing statements to next line 2023-08-15 18:16:14 -04:00
audit.h audit: correct audit_filter_inodes() definition 2023-07-21 12:17:25 -04:00
auditfilter.c audit: move trailing statements to next line 2023-08-15 18:16:14 -04:00
auditsc.c Including fixes from netfilter and bpf. 2023-09-07 18:33:07 -07:00
backtracetest.c
bounds.c
capability.c lsm: constify the 'target' parameter in security_capget() 2023-08-08 16:48:47 -04:00
cfi.c
compat.c sched_getaffinity: don't assume 'cpumask_size()' is fully initialized 2023-03-14 19:32:38 -07:00
configs.c
context_tracking.c locking/atomic: treewide: use raw_atomic*_<op>() 2023-06-05 09:57:20 +02:00
cpu_pm.c
cpu.c cpu/hotplug: Prevent self deadlock on CPU hot-unplug 2023-08-30 12:24:22 +02:00
crash_core.c Crash: add lock to serialize crash hotplug handling 2023-09-29 17:20:48 -07:00
crash_dump.c
cred.c cred: convert printks to pr_<level> 2023-08-18 10:18:49 -07:00
delayacct.c delayacct: track delays from IRQ/SOFTIRQ 2023-04-18 16:39:34 -07:00
dma.c
exec_domain.c
exit.c fork, vhost: Use CLONE_THREAD to fix freezer/ps regression 2023-06-01 17:15:33 -04:00
extable.c
fail_function.c kernel/fail_function: fix memory leak with using debugfs_lookup() 2023-02-08 13:36:22 +01:00
fork.c percpu: changes for v6.6 2023-09-01 15:44:45 -07:00
freezer.c
gen_kheaders.sh Revert "kheaders: substituting --sort in archive creation" 2023-05-28 16:20:21 +09:00
groups.c
hung_task.c kernel/hung_task.c: set some hung_task.c variables storage-class-specifier to static 2023-04-08 13:45:37 -07:00
iomem.c kernel/iomem.c: remove __weak ioremap_cache helper 2023-08-21 13:37:28 -07:00
irq_work.c trace: Add trace_ipi_send_cpu() 2023-03-24 11:01:29 +01:00
jump_label.c
kallsyms_internal.h
kallsyms_selftest.c Modules changes for v6.6-rc1 2023-08-29 17:32:32 -07:00
kallsyms_selftest.h
kallsyms.c kallsyms: Change func signature for cleanup_symbol_name() 2023-08-25 15:00:36 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz
Kconfig.kexec crash: hotplug support for kexec_load() 2023-08-24 16:25:14 -07:00
Kconfig.locks
Kconfig.preempt
kcov.c kcov: add prototypes for helper functions 2023-06-09 17:44:17 -07:00
kexec_core.c crash: add generic infrastructure for crash hotplug support 2023-08-24 16:25:13 -07:00
kexec_elf.c
kexec_file.c integrity-v6.6 2023-08-30 09:16:56 -07:00
kexec_internal.h
kexec.c crash: hotplug support for kexec_load() 2023-08-24 16:25:14 -07:00
kheaders.c kheaders: Use array declaration instead of char 2023-03-24 20:10:59 -07:00
kprobes.c kernel: kprobes: Use struct_size() 2023-08-23 09:38:17 +09:00
ksyms_common.c kallsyms: make kallsyms_show_value() as generic function 2023-06-08 12:27:20 -07:00
ksysfs.c crash: hotplug support for kexec_load() 2023-08-24 16:25:14 -07:00
kthread.c kthread: unexport __kthread_should_park() 2023-08-18 10:18:59 -07:00
latencytop.c
Makefile v6.5-rc1-modules-next 2023-06-28 15:51:08 -07:00
module_signature.c
notifier.c notifiers: add tracepoints to the notifiers infrastructure 2023-04-08 13:45:38 -07:00
nsproxy.c nsproxy: Convert nsproxy.count to refcount_t 2023-08-21 11:29:12 -07:00
padata.c padata: use alignment when calculating the number of worker threads 2023-03-14 17:06:44 +08:00
panic.c panic: Reenable preemption in WARN slowpath 2023-09-15 11:28:08 +02:00
params.c kernel: params: Remove unnecessary ‘0’ values from err 2023-07-10 12:47:01 -07:00
pid_namespace.c memfd: replace ratcheting feature from vm.memfd_noexec with hierarchy 2023-08-21 13:37:59 -07:00
pid_sysctl.h memfd: replace ratcheting feature from vm.memfd_noexec with hierarchy 2023-08-21 13:37:59 -07:00
pid.c pidfd: prevent a kernel-doc warning 2023-09-19 13:21:33 -07:00
profile.c
ptrace.c ptrace: Provide set/get interface for syscall user dispatch 2023-04-16 14:23:07 +02:00
range.c
reboot.c
regset.c
relay.c kernel: relay: remove unnecessary NULL values from relay_open_buf 2023-08-18 10:18:55 -07:00
resource_kunit.c
resource.c dax/kmem: Fix leak of memory-hotplug resources 2023-02-17 14:58:01 -08:00
rseq.c
scftorture.c scftorture: Pause testing after memory-allocation failure 2023-07-14 15:02:57 -07:00
scs.c
seccomp.c seccomp: Add missing kerndoc notations 2023-08-17 12:32:15 -07:00
signal.c signal: print comm and exe name on fatal signals 2023-08-18 10:18:50 -07:00
smp.c smp: Reduce NMI traffic from CSD waiters to CSD destination 2023-07-10 14:19:04 -07:00
smpboot.c cpu/hotplug: Remove unused state functions 2023-05-15 13:45:00 +02:00
smpboot.h
softirq.c sched/core: introduce sched_core_idle_cpu() 2023-07-13 15:21:50 +02:00
stackleak.c stackleak: allow to specify arch specific stackleak poison function 2023-04-20 11:36:35 +02:00
stacktrace.c
static_call_inline.c
static_call.c
stop_machine.c
sys_ni.c x86/shstk: Introduce map_shadow_stack syscall 2023-08-02 15:01:51 -07:00
sys.c prctl: move PR_GET_AUXV out of PR_MCE_KILL 2023-07-17 12:53:21 -07:00
sysctl-test.c
sysctl.c v6.5-rc1-sysctl-next 2023-06-28 16:05:21 -07:00
task_work.c task_work: add kerneldoc annotation for 'data' argument 2023-09-19 13:21:32 -07:00
taskstats.c
torture.c torture: Stop right-shifting torture_random() return values 2023-08-14 15:01:08 -07:00
tracepoint.c tracepoint: Allow livepatch module add trace event 2023-02-18 14:34:36 -05:00
tsacct.c
ucount.c sysctl: Add size to register_sysctl 2023-08-15 15:26:17 -07:00
uid16.c
uid16.h
umh.c sysctl: fix unused proc_cap_handler() function warning 2023-06-29 15:19:43 -07:00
up.c
user_namespace.c userns: fix a struct's kernel-doc notation 2023-02-02 22:50:04 -08:00
user-return-notifier.c
user.c
usermode_driver.c
utsname_sysctl.c utsname: simplify one-level sysctl registration for uts_kern_table 2023-04-13 11:49:35 -07:00
utsname.c
vhost_task.c vhost: Fix worker hangs due to missed wake up calls 2023-06-08 15:43:09 -04:00
watch_queue.c watch_queue: prevent dangling pipe pointer 2023-06-06 10:47:04 +02:00
watchdog_buddy.c watchdog/hardlockup: move SMP barriers from common code to buddy code 2023-06-19 16:25:28 -07:00
watchdog_perf.c watchdog/perf: add a weak function for an arch to detect if perf can use NMIs 2023-06-09 17:44:21 -07:00
watchdog.c watchdog/hardlockup: avoid large stack frames in watchdog_hardlockup_check() 2023-08-18 10:19:00 -07:00
workqueue_internal.h workqueue: Drop the special locking rule for worker->flags and worker_pool->flags 2023-08-07 15:57:22 -10:00
workqueue.c workqueue: Fix missed pwq_release_worker creation in wq_cpu_intensive_thresh_init() 2023-09-18 08:50:31 -10:00