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Trond Myklebust bf294b41ce SUNRPC: Close a race in __rpc_wait_for_completion_task() 
Although they run as rpciod background tasks, under normal operation
(i.e. no SIGKILL), functions like nfs_sillyrename(), nfs4_proc_unlck()
and nfs4_do_close() want to be fully synchronous. This means that when we
exit, we want all references to the rpc_task to be gone, and we want
any dentry references etc. held by that task to be released.

For this reason these functions call __rpc_wait_for_completion_task(),
followed by rpc_put_task() in the expectation that the latter will be
releasing the last reference to the rpc_task, and thus ensuring that the
callback_ops->rpc_release() has been called synchronously.

This patch fixes a race which exists due to the fact that
rpciod calls rpc_complete_task() (in order to wake up the callers of
__rpc_wait_for_completion_task()) and then subsequently calls
rpc_put_task() without ensuring that these two steps are done atomically.

In order to avoid adding new spin locks, the patch uses the existing
waitqueue spin lock to order the rpc_task reference count releases between
the waiting process and rpciod.
The common case where nobody is waiting for completion is optimised for by
checking if the RPC_TASK_ASYNC flag is cleared and/or if the rpc_task
reference count is 1: in those cases we drop trying to grab the spin lock,
and immediately free up the rpc_task.

Those few processes that need to put the rpc_task from inside an
asynchronous context and that do not care about ordering are given a new
helper: rpc_put_task_async().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
2011-03-10 15:04:52 -05:00
..
debug Merge branch 'master' into for-next 2010-12-22 18:57:02 +01:00
gcov
irq genirq: Disable the SHIRQ_DEBUG call in request_threaded_irq for now 2011-02-19 12:11:13 +01:00
power Merge branch 'fixes-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq 2011-02-18 12:36:06 -08:00
time clockevents: Prevent oneshot mode when broadcast device is periodic 2011-02-26 09:45:28 +01:00
trace blktrace: Remove blk_fill_rwbs_rq. 2011-03-03 10:53:20 -05:00
.gitignore
acct.c
async.c
audit.c
audit.h
audit_tree.c
audit_watch.c
auditfilter.c
auditsc.c
backtracetest.c
bounds.c
capability.c security: add cred argument to security_capable() 2011-02-11 17:41:58 +11:00
cgroup.c Merge branch 'vfs-scale-working' of git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin 2011-01-14 09:08:29 -08:00
cgroup_freezer.c
compat.c
configs.c
cpu.c Merge branches 'x86-alternatives-for-linus', 'x86-fpu-for-linus', 'x86-hwmon-for-linus', 'x86-paravirt-for-linus', 'core-locking-for-linus' and 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-01-06 11:11:50 -08:00
cpuset.c cpuset: add a missing unlock in cpuset_write_resmask() 2011-03-04 17:53:38 -08:00
cred.c CRED: Fix memory and refcount leaks upon security_prepare_creds() failure 2011-02-07 14:04:00 -08:00
delayacct.c
dma.c
elfcore.c
exec_domain.c
exit.c Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-01-11 11:02:13 -08:00
extable.c
fork.c thp: khugepaged 2011-01-13 17:32:43 -08:00
freezer.c Freezer: Fix a race during freezing of TASK_STOPPED tasks 2010-12-24 15:02:40 +01:00
futex.c Merge branches 'core-fixes-for-linus', 'x86-fixes-for-linus', 'timers-fixes-for-linus' and 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-01-15 12:45:00 -08:00
futex_compat.c
groups.c
hrtimer.c Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
hung_task.c
hw_breakpoint.c
irq_work.c irq_work: Use per cpu atomics instead of regular atomics 2010-12-18 15:54:48 +01:00
itimer.c
jump_label.c
kallsyms.c
Kconfig.freezer
Kconfig.hz
Kconfig.locks
Kconfig.preempt
kexec.c
kfifo.c
kmod.c
kprobes.c Merge branch 'for-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu 2011-01-07 17:02:58 -08:00
ksysfs.c
kthread.c sched: Constify function scope static struct sched_param usage 2011-01-07 15:55:45 +01:00
latencytop.c fs/proc/base.c, kernel/latencytop.c: convert sprintf_symbol() to %ps 2011-01-13 08:03:16 -08:00
lockdep.c lockdep: Move early boot local IRQ enable/disable status to init/main.c 2011-01-20 13:32:33 +01:00
lockdep_internals.h
lockdep_proc.c
lockdep_states.h
Makefile kernel: clean up USE_GENERIC_SMP_HELPERS 2011-01-13 08:03:08 -08:00
module.c tracepoints: Fix section alignment using pointer array 2011-02-03 09:28:46 -05:00
mutex-debug.c
mutex-debug.h
mutex.c
mutex.h
notifier.c
ns_cgroup.c
nsproxy.c
padata.c
panic.c ACPI, APEI, Generic Hardware Error Source POLL/IRQ/NMI notification type support 2011-01-12 03:06:19 -05:00
params.c module: show version information for built-in modules in sysfs 2011-01-24 14:32:51 +10:30
perf_event.c perf: Fix throttle logic 2011-02-16 13:25:29 +01:00
pid.c
pid_namespace.c
pm_qos_params.c
posix-cpu-timers.c
posix-timers.c
printk.c cap_syslog: accept CAP_SYS_ADMIN for now 2011-02-10 17:53:55 -08:00
profile.c
ptrace.c Mark ptrace_{traceme,attach,detach} static 2011-03-04 09:23:30 -08:00
range.c
rcupdate.c
rcutiny.c rcu: avoid pointless blocked-task warnings 2011-01-14 04:58:08 -08:00
rcutiny_plugin.h
rcutorture.c
rcutree.c Merge branch 'for-2.6.38' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/percpu 2011-01-07 17:02:58 -08:00
rcutree.h rcu: limit rcu_node leaf-level fanout 2010-12-17 12:34:20 -08:00
rcutree_plugin.h rcu: increase synchronize_sched_expedited() batching 2010-12-17 12:34:08 -08:00
rcutree_trace.c
relay.c
res_counter.c
resource.c
rtmutex-debug.c
rtmutex-debug.h
rtmutex-tester.c
rtmutex.c
rtmutex.h
rtmutex_common.h
rwsem.c
sched.c SUNRPC: Close a race in __rpc_wait_for_completion_task() 2011-03-10 15:04:52 -05:00
sched_autogroup.c sched, autogroup: Fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure 2011-01-18 15:09:42 +01:00
sched_autogroup.h sched, autogroup: Fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure 2011-01-18 15:09:42 +01:00
sched_clock.c
sched_cpupri.c
sched_cpupri.h
sched_debug.c sched: Replace rq->bkl_count with rq->rq_sched_info.bkl_count 2011-01-18 15:09:43 +01:00
sched_fair.c sched: Use rq->clock_task instead of rq->clock for correctly maintaining load averages 2011-01-26 12:31:03 +01:00
sched_features.h
sched_idletask.c
sched_rt.c sched: Fix update_curr_rt() 2011-02-03 12:21:33 +01:00
sched_stats.h
sched_stoptask.c
seccomp.c
semaphore.c
signal.c
smp.c Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2011-01-20 18:30:37 -08:00
softirq.c kernel: clean up USE_GENERIC_SMP_HELPERS 2011-01-13 08:03:08 -08:00
spinlock.c
srcu.c rcu: demote SRCU_SYNCHRONIZE_DELAY from kernel-parameter status 2011-01-14 04:56:49 -08:00
stacktrace.c
stop_machine.c
sys.c Fix prlimit64 for suid/sgid processes 2011-01-31 13:01:27 +10:00
sys_ni.c
sysctl.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2011-01-26 16:31:44 +10:00
sysctl_binary.c Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2011-01-13 10:05:56 -08:00
sysctl_check.c
taskstats.c taskstats: use better ifdef for alignment 2011-01-13 08:03:19 -08:00
test_kprobes.c
time.c
timeconst.pl
timer.c Revert "lockdep, timer: Fix del_timer_sync() annotation" 2011-02-08 16:18:39 +01:00
tracepoint.c tracepoints: Fix section alignment using pointer array 2011-02-03 09:28:46 -05:00
tsacct.c
uid16.c
up.c
user-return-notifier.c
user.c fix freeing user_struct in user cache 2010-12-29 11:31:38 -08:00
user_namespace.c user_ns: improve the user_ns on-the-slab packaging 2011-01-13 08:03:18 -08:00
utsname.c
utsname_sysctl.c
wait.c
watchdog.c watchdog, nmi: Lower the severity of error messages 2011-02-10 13:21:59 +01:00
workqueue.c workqueue: make sure MAYDAY_INITIAL_TIMEOUT is at least 2 jiffies long 2011-02-16 18:10:19 +01:00
workqueue_sched.h