forked from Minki/linux
staging: comedi: remain busy until read end-of-file
If a COMEDI subdevice is busy handling an asynchronous command in the "read" direction, then after the command has terminated itself, the "read" file operation handler, `comedi_read()` should keep the subdevice busy until all available data has been read and it has returned 0 to indicate an "end-of-file" condition. Currently, it has a bug where it can mark the subdevice as non-busy even when returning a non-zero count. The bug is slightly hidden because the next "read" will return 0 because the subdevice is no longer busy. Fix it by checking the return count is 0 before deciding to mark the subdevice as non-busy. The call to `comedi_is_subdevice_idle()` is superfluous as the `become_nonbusy` variable will have been set to `true` when considering becoming non-busy. Strictly speaking, checking the return count is superfluous too, as `become_nonbusy` doesn't get set to `true` unless the count is 0, but check the return count anyway to make the intention clearer. Signed-off-by: Ian Abbott <abbotti@mev.co.uk> Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -2551,7 +2551,7 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
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}
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remove_wait_queue(&async->wait_head, &wait);
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set_current_state(TASK_RUNNING);
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if (become_nonbusy || comedi_is_subdevice_idle(s)) {
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if (become_nonbusy && count == 0) {
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struct comedi_subdevice *new_s;
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/*
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