Commit Graph

12 Commits

Author SHA1 Message Date
Paolo Bonzini e11131b025 rcu: simplify memory barriers
Thanks to the acquire semantics of qemu_event_reset and qemu_event_wait,
some memory barriers can be removed.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2016-10-24 11:30:56 +02:00
Peter Maydell aafd758410 util: Clean up includes
Clean up includes so that osdep.h is included first and headers
which it implies are not included manually.

This commit was created with scripts/clean-includes.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1454089805-5470-6-git-send-email-peter.maydell@linaro.org
2016-02-04 17:01:04 +00:00
Paolo Bonzini 05620f85e9 Revert "rcu: init rcu_registry_lock after fork"
This reverts commit 5243722376.
The patch forgot about rcu_sync_lock and was committed by mistake.

Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-09-16 17:33:32 +02:00
Emilio G. Cota 5243722376 rcu: init rcu_registry_lock after fork
We were unlocking this lock after fork, which is wrong since
only the thread that holds a mutex is allowed to unlock it.

Signed-off-by: Emilio G. Cota <cota@braap.org>
Message-Id: <1440375847-17603-9-git-send-email-cota@braap.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-09-09 15:34:54 +02:00
Wen Congyang c097a60b10 rcu: Allow calling rcu_(un)register_thread() during synchronize_rcu()
If rcu_(un)register_thread() is called together with synchronize_rcu(),
it will wait for the synchronize_rcu() to finish. But when synchronize_rcu()
waits for some events, we can modify the list registry.
We also use the lock rcu_gp_lock to assume that synchronize_rcu() isn't
executed in more than one thread at the same time. Add a new mutex lock
rcu_sync_lock to assume it and rename rcu_gp_lock to rcu_registry_lock.
Release rcu_registry_lock when synchronize_rcu() waits for some events.

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Message-Id: <55B59652.4090503@cn.fujitsu.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-08-14 23:40:32 +02:00
Paolo Bonzini ab28bd2312 rcu: actually register threads that have RCU read-side critical sections
Otherwise, grace periods are detected too early!

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-07-24 13:57:45 +02:00
Paolo Bonzini a59629fcc6 rcu: do not create thread in pthread_atfork callback
If QEMU forks after the CPU threads have been created, qemu_mutex_lock_iothread
will not be able to do qemu_cpu_kick_thread.  There is no solution other than
assuming that forks after the CPU threads have been created will end up in an
exec.  Forks before the CPU threads have been created (such as -daemonize)
have to call rcu_after_fork manually.

Notably, the oxygen theme for GTK+ forks and shows a "No such process" error
without this patch.

This patch can be reverted once the iothread loses the "kick the TCG thread"
magic.

User-mode emulation does not use the iothread, so it can also call
rcu_after_fork.

Reported by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-04-01 10:06:38 +02:00
Paolo Bonzini 21b7cf9e07 rcu: handle forks safely
After forking, only the calling thread is duplicated in the child process.
The call_rcu thread has to be recreated in the child.  Exploit the fact
that only one thread exists (same as when constructors run), and just redo
the entire initialization to ensure the threads are in the proper state.

The only additional things to do are emptying the list of threads
registered with RCU, and unlocking the lock that was taken in the prepare
callback (implementations are allowed to fail pthread_mutex_init()
if the mutex is still locked).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-03-10 10:49:25 +01:00
Paolo Bonzini a464982499 rcu: run RCU callbacks under the BQL
This needs to go away sooner or later, but one complication is the
complex VFIO data structures that are modified in instance_finalize.
Take a shortcut for now.

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-02-11 21:48:40 +01:00
Paolo Bonzini a7d1d63679 rcu: do not let RCU callbacks pile up indefinitely
Always process them within a short time.  Even though waiting a little
is useful, it is not okay to delay e.g. qemu_opts_del forever.

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Tested-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-02-11 21:48:37 +01:00
Paolo Bonzini 26387f86c9 rcu: add call_rcu
Asynchronous callbacks provided by call_rcu are particularly important
for QEMU, because the BQL makes it hard to use synchronize_rcu.

In addition, the current RCU implementation is not particularly friendly
to multiple concurrent synchronize_rcu callers, making call_rcu even
more important.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-02-02 16:55:10 +01:00
Paolo Bonzini 7911747bd4 rcu: add rcu library
This includes a (mangled) copy of the liburcu code.  The main changes
are: 1) removing dependencies on many other header files in liburcu; 2)
removing for simplicity the tentative busy waiting in synchronize_rcu,
which has limited performance effects; 3) replacing futexes in
synchronize_rcu with QemuEvents for Win32 portability.  The API is
the same as liburcu, so it should be possible in the future to require
liburcu on POSIX systems for example and use our copy only on Windows.

Among the various versions available I chose urcu-mb, which is the
least invasive implementation even though it does not have the
fastest rcu_read_{lock,unlock} implementation.  The urcu flavor can
be changed later, after benchmarking.

Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2015-02-02 16:55:10 +01:00