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cb424ffe9f
kernel_optimize_test/kernel
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Kay Sievers cb424ffe9f kmsg: properly handle concurrent non-blocking read() from /proc/kmsg 
The /proc/kmsg read() interface is internally simply wired up to a sequence
of syslog() syscalls, which might are racy between their checks and actions,
regarding concurrency.

In the (very uncommon) case of concurrent readers of /dev/kmsg, relying on
usual O_NONBLOCK behavior, the recently introduced mutex might block an
O_NONBLOCK reader in read(), when poll() returns for it, but another process
has already read the data in the meantime. We've seen that while running
artificial test setups and tools that "fight" about /proc/kmsg data.

This restores the original /proc/kmsg behavior, where in case of concurrent
read()s, poll() might wake up but the read() syscall will just return 0 to
the caller, while another process has "stolen" the data.

This is in the general case not the expected behavior, but it is the exact
same one, that can easily be triggered with a 3.4 kernel, and some tools
might just rely on it.

The mutex is not needed, the original integrity issue which introduced it,
is in the meantime covered by:
  "fill buffer with more than a single message for SYSLOG_ACTION_READ"
  116e90b23f

Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Kay Sievers <kay@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2012-07-06 09:50:09 -07:00
..
debug KGDB/KDB regression fixes 2012-04-04 17:26:08 -07:00
events perf: Use css_tryget() to avoid propping up css refcount 2012-06-18 11:45:57 +02:00
gcov
irq Merge branches 'irq-urgent-for-linus' and 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-06-04 11:36:51 -07:00
power PM / Hibernate: Use get_gendisk to verify partition if resume_file is integer format 2012-05-18 20:44:59 +02:00
sched Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-06-08 14:59:29 -07:00
time Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2012-06-15 16:52:35 -07:00
trace tracing: Have tracing_off() actually turn tracing off 2012-06-06 22:15:14 -04:00
.gitignore
acct.c
async.c
audit_tree.c
audit_watch.c
audit.c
audit.h
auditfilter.c
auditsc.c seccomp: remove duplicated failure logging 2012-04-14 11:13:20 +10:00
backtracetest.c
bounds.c
capability.c userns: Teach inode_capable to understand inodes whose uids map to other namespaces. 2012-05-15 14:59:24 -07:00
cgroup_freezer.c cgroup: convert all non-memcg controllers to the new cftype interface 2012-04-01 12:09:55 -07:00
cgroup.c cgroups: Account for CSS_DEACT_BIAS in __css_put 2012-06-18 15:38:02 -07:00
compat.c new helper: sigsuspend() 2012-05-21 23:52:30 -04:00
configs.c
cpu_pm.c kernel/cpu_pm.c: fix various typos 2012-05-31 17:49:27 -07:00
cpu.c kernel/cpu.c: document clear_tasks_mm_cpumask() 2012-05-31 17:49:30 -07:00
cpuset.c Merge branch 'for-3.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2012-05-22 17:40:19 -07:00
crash_dump.c
cred.c keys: kill task_struct->replacement_session_keyring 2012-05-23 22:11:41 -04:00
delayacct.c
dma.c Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
elfcore.c
exec_domain.c
exit.c pidns: find_new_reaper() can no longer switch to init_pid_ns.child_reaper 2012-06-20 14:39:36 -07:00
extable.c extable: Skip sorting if sorted at build time. 2012-04-19 15:06:55 -07:00
fork.c Revert "mm: correctly synchronize rss-counters at exit/exec" 2012-06-07 17:54:07 -07:00
freezer.c
futex_compat.c futex: Mark get_robust_list as deprecated 2012-03-29 11:37:17 +02:00
futex.c futex: Mark get_robust_list as deprecated 2012-03-29 11:37:17 +02:00
groups.c userns: Convert in_group_p and in_egroup_p to use kgid_t 2012-05-03 03:29:33 -07:00
hrtimer.c
hung_task.c hung task debugging: Inject NMI when hung and going to panic 2012-04-25 12:39:25 +02:00
irq_work.c irq_work: fix compile failure on tile from missing include 2012-04-13 13:15:16 -04:00
itimer.c itimer: Use printk_once instead of WARN_ONCE 2012-04-10 11:00:30 +02:00
jump_label.c
kallsyms.c vsprintf: fix %ps on non symbols when using kallsyms 2012-05-29 16:22:32 -07:00
kcmp.c syscalls, x86: add __NR_kcmp syscall 2012-05-31 17:49:32 -07:00
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c Merge branch 'akpm' (Andrew's patch-bomb) 2012-03-28 17:19:28 -07:00
kfifo.c [media] kernel:kfifo: export __kfifo_max_r symbol 2012-04-11 18:24:37 -03:00
kmod.c kmod.c: fix kernel-doc warning 2012-05-31 17:49:28 -07:00
kprobes.c
ksysfs.c
kthread.c
latencytop.c
lglock.c brlocks/lglocks: turn into functions 2012-05-29 23:28:41 -04:00
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
lockdep.c
Makefile Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2012-06-01 10:34:35 -07:00
module.c Guard check in module loader against integer overflow 2012-05-23 22:28:53 +09:30
mutex-debug.c
mutex-debug.h
mutex.c
mutex.h
notifier.c
nsproxy.c
padata.c padata: Fix cpu hotplug 2012-03-29 19:52:46 +08:00
panic.c kdump: Execute kmsg_dump(KMSG_DUMP_PANIC) after smp_send_stop() 2012-05-18 14:02:10 +02:00
params.c params: replace printk(KERN_<LVL>...) with pr_<lvl>(...) 2012-05-04 17:28:18 -07:00
pid_namespace.c pidns: guarantee that the pidns init will be the last pidns process reaped 2012-06-20 14:39:36 -07:00
pid.c mm: add a low limit to alloc_large_system_hash 2012-05-24 00:28:21 -04:00
posix-cpu-timers.c
posix-timers.c
printk.c kmsg: properly handle concurrent non-blocking read() from /proc/kmsg 2012-07-06 09:50:09 -07:00
profile.c
ptrace.c userns: Convert ptrace, kill, set_priority permission checks to work with kuids and kgids 2012-05-03 03:28:51 -07:00
range.c
rcu.h
rcupdate.c rcu: Make exit_rcu() more precise and consolidate 2012-05-02 14:48:27 -07:00
rcutiny_plugin.h rcu: Make exit_rcu() more precise and consolidate 2012-05-02 14:48:27 -07:00
rcutiny.c
rcutorture.c rcu: Add rcutorture test for call_srcu() 2012-04-30 10:48:26 -07:00
rcutree_plugin.h rcu: Precompute RCU_FAST_NO_HZ timer offsets 2012-06-06 20:43:28 -07:00
rcutree_trace.c rcu: Make rcu_barrier() less disruptive 2012-05-09 14:27:54 -07:00
rcutree.c rcu: Stop rcu_do_batch() from multiplexing the "count" variable 2012-06-25 12:35:25 -07:00
rcutree.h rcu: Move RCU_FAST_NO_HZ per-CPU variables to rcu_dynticks structure 2012-06-06 20:43:28 -07:00
relay.c
res_counter.c rescounters: add res_counter_uncharge_until() 2012-05-29 16:22:27 -07:00
resource.c kernel/resource.c: correct the comment of allocate_resource() 2012-05-31 17:49:26 -07:00
rtmutex_common.h
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c
rtmutex.c
rtmutex.h
rwsem.c Remove all #inclusions of asm/system.h 2012-03-28 18:30:03 +01:00
seccomp.c seccomp: fix build warnings when there is no CONFIG_SECCOMP_FILTER 2012-04-18 12:24:52 +10:00
semaphore.c semaphore: fix improper comment reference to mutex 2012-04-05 17:15:55 -07:00
signal.c new helper: signal_delivered() 2012-06-01 12:58:52 -04:00
smp.c smp: Implement kick_all_cpus_sync() 2012-05-08 12:35:06 +02:00
smpboot.c smpboot, idle: Fix comment mismatch over idle_threads_init() 2012-05-24 22:58:08 +02:00
smpboot.h smp: Fix idle_thread_init() inline stub 2012-05-04 12:52:25 +02:00
softirq.c
spinlock.c
srcu.c rcu: Implement per-domain single-threaded call_srcu() state machine 2012-04-30 10:48:25 -07:00
stacktrace.c
stop_machine.c
sys_ni.c syscalls, x86: add __NR_kcmp syscall 2012-05-31 17:49:32 -07:00
sys.c c/r: prctl: Move PR_GET_TID_ADDRESS to a proper place 2012-06-20 14:39:36 -07:00
sysctl_binary.c
sysctl.c sysctl: fix write access to dmesg_restrict/kptr_restrict 2012-04-05 14:51:43 +10:00
task_work.c task_work_add: generic process-context callbacks 2012-05-23 22:09:21 -04:00
taskstats.c
test_kprobes.c
time.c
timeconst.pl
timer.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2012-05-23 17:42:39 -07:00
tracepoint.c
tsacct.c
uid16.c userns: Convert setting and getting uid and gid system calls to use kuid and kgid 2012-05-03 03:28:41 -07:00
up.c
user_namespace.c userns: Store uid and gid values in struct cred with kuid_t and kgid_t types 2012-05-03 03:28:38 -07:00
user-return-notifier.c
user.c userns: Silence silly gcc warning. 2012-05-19 15:44:40 -06:00
utsname_sysctl.c
utsname.c userns: Use cred->user_ns instead of cred->user->user_ns 2012-04-07 16:55:51 -07:00
wait.c
watchdog.c watchdog: Quiet down the boot messages 2012-06-14 12:20:50 +02:00
workqueue_sched.h
workqueue.c lockdep: fix oops in processing workqueue 2012-05-15 08:08:31 -07:00