fuse: allow interrupt queuing without fc->lock (8f7bb368) · Commits · 戴 / test

Interrupt is only queued after the request has been sent to userspace. This is either done in request_wait_answer() or fuse_dev_do_read() depending on which state the request is in at the time of the interrupt. If it's not yet sent, then queuing the interrupt is postponed until the request is read. Otherwise (the request has already been read and is waiting for an answer) the interrupt is queued immedidately. We want to call queue_interrupt() without fc->lock protection, in which case there can be a race between the two functions: - neither of them queue the interrupt (thinking the other one has already done it). - both of them queue the interrupt The first one is prevented by adding memory barriers, the second is prevented by checking (under fiq->waitq.lock) if the interrupt has already been queued. Signed-off-by:

Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/dev.c

+9 −3

Original line number	Diff line number	Diff line
		@@ -423,8 +423,10 @@ __releases(fc->lock)
		static void queue_interrupt(struct fuse_iqueue fiq, struct fuse_req req)
		{
		spin_lock(&fiq->waitq.lock);
		if (list_empty(&req->intr_entry)) {
		list_add_tail(&req->intr_entry, &fiq->interrupts);
		wake_up_locked(&fiq->waitq);
		}
		spin_unlock(&fiq->waitq.lock);
		kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
		}
		@@ -443,6 +445,8 @@ static void request_wait_answer(struct fuse_conn fc, struct fuse_req req)

		spin_lock(&fc->lock);
		set_bit(FR_INTERRUPTED, &req->flags);
		/* matches barrier in fuse_dev_do_read() */
		smp_mb__after_atomic();
		if (test_bit(FR_SENT, &req->flags))
		queue_interrupt(fiq, req);
		spin_unlock(&fc->lock);
		@@ -1358,8 +1362,10 @@ static ssize_t fuse_dev_do_read(struct fuse_conn fc, struct file file,
		if (!test_bit(FR_ISREPLY, &req->flags)) {
		request_end(fc, req);
		} else {
		set_bit(FR_SENT, &req->flags);
		list_move_tail(&req->list, &fc->processing);
		set_bit(FR_SENT, &req->flags);
		/* matches barrier in request_wait_answer() */
		smp_mb__after_atomic();
		if (test_bit(FR_INTERRUPTED, &req->flags))
		queue_interrupt(fiq, req);
		spin_unlock(&fc->lock);

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