3.18.18-rt16-rc1 stable review patch. If anyone has any objections, please let me know. ------------------ From: Davidlohr Bueso <dave@xxxxxxxxxxxx> This patch moves the wakeup_process() invocation so it is not done under the info->lock by making use of a lockless wake_q. With this change, the waiter is woken up once it is STATE_READY and it does not need to loop on SMP if it is still in STATE_PENDING. In the timeout case we still need to grab the info->lock to verify the state. This change should also avoid the introduction of preempt_disable() in -rt which avoids a busy-loop which pools for the STATE_PENDING -> STATE_READY change if the waiter has a higher priority compared to the waker. Additionally, this patch micro-optimizes wq_sleep by using the cheaper cousin of set_current_state(TASK_INTERRUPTABLE) as we will block no matter what, thus get rid of the implied barrier. Cc: stable-rt@xxxxxxxxxxxxxxx Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Acked-by: George Spelvin <linux@xxxxxxxxxxx> Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Chris Mason <clm@xxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: dave@xxxxxxxxxxxx Link: http://lkml.kernel.org/r/1430748166.1940.17.camel@xxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> --- ipc/mqueue.c | 53 ++++++++++++++++++++++++++++++++--------------------- 1 file changed, 32 insertions(+), 21 deletions(-) diff --git a/ipc/mqueue.c b/ipc/mqueue.c index 516902313dc3..79351b5dd0a1 100644 --- a/ipc/mqueue.c +++ b/ipc/mqueue.c @@ -47,8 +47,7 @@ #define RECV 1 #define STATE_NONE 0 -#define STATE_PENDING 1 -#define STATE_READY 2 +#define STATE_READY 1 struct posix_msg_tree_node { struct rb_node rb_node; @@ -571,15 +570,12 @@ static int wq_sleep(struct mqueue_inode_info *info, int sr, wq_add(info, sr, ewp); for (;;) { - set_current_state(TASK_INTERRUPTIBLE); + __set_current_state(TASK_INTERRUPTIBLE); spin_unlock(&info->lock); time = schedule_hrtimeout_range_clock(timeout, 0, HRTIMER_MODE_ABS, CLOCK_REALTIME); - while (ewp->state == STATE_PENDING) - cpu_relax(); - if (ewp->state == STATE_READY) { retval = 0; goto out; @@ -907,11 +903,15 @@ out_name: * list of waiting receivers. A sender checks that list before adding the new * message into the message array. If there is a waiting receiver, then it * bypasses the message array and directly hands the message over to the - * receiver. - * The receiver accepts the message and returns without grabbing the queue - * spinlock. Therefore an intermediate STATE_PENDING state and memory barriers - * are necessary. The same algorithm is used for sysv semaphores, see - * ipc/sem.c for more details. + * receiver. The receiver accepts the message and returns without grabbing the + * queue spinlock: + * + * - Set pointer to message. + * - Queue the receiver task for later wakeup (without the info->lock). + * - Update its state to STATE_READY. Now the receiver can continue. + * - Wake up the process after the lock is dropped. Should the process wake up + * before this wakeup (due to a timeout or a signal) it will either see + * STATE_READY and continue or acquire the lock to check the state again. * * The same algorithm is used for senders. */ @@ -919,7 +919,8 @@ out_name: /* pipelined_send() - send a message directly to the task waiting in * sys_mq_timedreceive() (without inserting message into a queue). */ -static inline void pipelined_send(struct mqueue_inode_info *info, +static inline void pipelined_send(struct wake_q_head *wake_q, + struct mqueue_inode_info *info, struct msg_msg *message, struct ext_wait_queue *receiver) { @@ -929,16 +930,23 @@ static inline void pipelined_send(struct mqueue_inode_info *info, preempt_disable_rt(); receiver->msg = message; list_del(&receiver->list); - receiver->state = STATE_PENDING; - wake_up_process(receiver->task); - smp_wmb(); + wake_q_add(wake_q, receiver->task); + /* + * Rely on the implicit cmpxchg barrier from wake_q_add such + * that we can ensure that updating receiver->state is the last + * write operation: As once set, the receiver can continue, + * and if we don't have the reference count from the wake_q, + * yet, at that point we can later have a use-after-free + * condition and bogus wakeup. + */ receiver->state = STATE_READY; preempt_enable_rt(); } /* pipelined_receive() - if there is task waiting in sys_mq_timedsend() * gets its message and put to the queue (we have one free place for sure). */ -static inline void pipelined_receive(struct mqueue_inode_info *info) +static inline void pipelined_receive(struct wake_q_head *wake_q, + struct mqueue_inode_info *info) { struct ext_wait_queue *sender = wq_get_first_waiter(info, SEND); @@ -953,9 +961,7 @@ static inline void pipelined_receive(struct mqueue_inode_info *info) preempt_disable_rt(); if (!msg_insert(sender->msg, info)) { list_del(&sender->list); - sender->state = STATE_PENDING; - wake_up_process(sender->task); - smp_wmb(); + wake_q_add(wake_q, sender->task); sender->state = STATE_READY; } preempt_enable_rt(); @@ -975,6 +981,7 @@ SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr, struct timespec ts; struct posix_msg_tree_node *new_leaf = NULL; int ret = 0; + WAKE_Q(wake_q); if (u_abs_timeout) { int res = prepare_timeout(u_abs_timeout, &expires, &ts); @@ -1059,7 +1066,7 @@ SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr, } else { receiver = wq_get_first_waiter(info, RECV); if (receiver) { - pipelined_send(info, msg_ptr, receiver); + pipelined_send(&wake_q, info, msg_ptr, receiver); } else { /* adds message to the queue */ ret = msg_insert(msg_ptr, info); @@ -1072,6 +1079,7 @@ SYSCALL_DEFINE5(mq_timedsend, mqd_t, mqdes, const char __user *, u_msg_ptr, } out_unlock: spin_unlock(&info->lock); + wake_up_q(&wake_q); out_free: if (ret) free_msg(msg_ptr); @@ -1159,14 +1167,17 @@ SYSCALL_DEFINE5(mq_timedreceive, mqd_t, mqdes, char __user *, u_msg_ptr, msg_ptr = wait.msg; } } else { + WAKE_Q(wake_q); + msg_ptr = msg_get(info); inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME; /* There is now free space in queue. */ - pipelined_receive(info); + pipelined_receive(&wake_q, info); spin_unlock(&info->lock); + wake_up_q(&wake_q); ret = 0; } if (ret == 0) { -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe stable-rt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
