From c1d51dd505577b189bf33867a9c20015ca7efb46 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 21 Mar 2020 12:25:47 +0100 Subject: usb: gadget: Use completion interface instead of open coding it ep_io() uses a completion on stack and open codes the waiting with: wait_event_interruptible (done.wait, done.done); and wait_event (done.wait, done.done); This waits in non-exclusive mode for complete(), but there is no reason to do so because the completion can only be waited for by the task itself and complete() wakes exactly one exlusive waiter. Replace the open coded implementation with the corresponding wait_for_completion*() functions. No functional change. Reported-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Greg Kroah-Hartman Link: https://lkml.kernel.org/r/20200321113241.043380271@linutronix.de --- drivers/usb/gadget/legacy/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'drivers/usb') diff --git a/drivers/usb/gadget/legacy/inode.c b/drivers/usb/gadget/legacy/inode.c index b47938dff1a2..4c3aff987289 100644 --- a/drivers/usb/gadget/legacy/inode.c +++ b/drivers/usb/gadget/legacy/inode.c @@ -344,7 +344,7 @@ ep_io (struct ep_data *epdata, void *buf, unsigned len) spin_unlock_irq (&epdata->dev->lock); if (likely (value == 0)) { - value = wait_event_interruptible (done.wait, done.done); + value = wait_for_completion_interruptible(&done); if (value != 0) { spin_lock_irq (&epdata->dev->lock); if (likely (epdata->ep != NULL)) { @@ -353,7 +353,7 @@ ep_io (struct ep_data *epdata, void *buf, unsigned len) usb_ep_dequeue (epdata->ep, epdata->req); spin_unlock_irq (&epdata->dev->lock); - wait_event (done.wait, done.done); + wait_for_completion(&done); if (epdata->status == -ECONNRESET) epdata->status = -EINTR; } else { -- cgit v1.2.3 From a5c6234e10280b3ec65e2410ce34904a2580e5f8 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sat, 21 Mar 2020 12:26:00 +0100 Subject: completion: Use simple wait queues completion uses a wait_queue_head_t to enqueue waiters. wait_queue_head_t contains a spinlock_t to protect the list of waiters which excludes it from being used in truly atomic context on a PREEMPT_RT enabled kernel. The spinlock in the wait queue head cannot be replaced by a raw_spinlock because: - wait queues can have custom wakeup callbacks, which acquire other spinlock_t locks and have potentially long execution times - wake_up() walks an unbounded number of list entries during the wake up and may wake an unbounded number of waiters. For simplicity and performance reasons complete() should be usable on PREEMPT_RT enabled kernels. completions do not use custom wakeup callbacks and are usually single waiter, except for a few corner cases. Replace the wait queue in the completion with a simple wait queue (swait), which uses a raw_spinlock_t for protecting the waiter list and therefore is safe to use inside truly atomic regions on PREEMPT_RT. There is no semantical or functional change: - completions use the exclusive wait mode which is what swait provides - complete() wakes one exclusive waiter - complete_all() wakes all waiters while holding the lock which protects the wait queue against newly incoming waiters. The conversion to swait preserves this behaviour. complete_all() might cause unbound latencies with a large number of waiters being woken at once, but most complete_all() usage sites are either in testing or initialization code or have only a really small number of concurrent waiters which for now does not cause a latency problem. Keep it simple for now. The fixup of the warning check in the USB gadget driver is just a straight forward conversion of the lockless waiter check from one waitqueue type to the other. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Greg Kroah-Hartman Reviewed-by: Davidlohr Bueso Reviewed-by: Joel Fernandes (Google) Acked-by: Linus Torvalds Link: https://lkml.kernel.org/r/20200321113242.317954042@linutronix.de --- drivers/usb/gadget/function/f_fs.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/usb') diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 571917677d35..234177dd1ed5 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1703,7 +1703,7 @@ static void ffs_data_put(struct ffs_data *ffs) pr_info("%s(): freeing\n", __func__); ffs_data_clear(ffs); BUG_ON(waitqueue_active(&ffs->ev.waitq) || - waitqueue_active(&ffs->ep0req_completion.wait) || + swait_active(&ffs->ep0req_completion.wait) || waitqueue_active(&ffs->wait)); destroy_workqueue(ffs->io_completion_wq); kfree(ffs->dev_name); -- cgit v1.2.3