Messages in this thread | | | Date | Mon, 10 Apr 2017 19:48:30 -0400 | From | Dave Jones <> | Subject | Re: iov_iter_pipe warning. |
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On Mon, Apr 10, 2017 at 08:57:11PM +0100, Al Viro wrote: > On Mon, Apr 10, 2017 at 03:42:06PM -0400, Dave Jones wrote: > > > Do you have a reliable reproducer? > > > > Not reliable, but I'll see if I can find some time to narrow it down > > this week. I've been working on better logging of "wtf just happened" > > the last few weeks, so it should get easier once I finish that work. > > I would suggest > a) slapping WARN_ON(pipe->nr_bufs); right before the loop > in splice_direct_to_actor(). Internal pipe should be empty when we > enter this function. > b) the same WARN_ON() in the very end of the loop body. > > We should have started with empty pipe. We'd called ->splice_read() > and it had returned a positive number (in read_len). That should be > the amount we'd pushed in there. Then we call actor(), with > sd->total_len set to read_len. Its return value is > * positive (or we would've buggered off) > * no less than read_len (ditto) > so it should have drained the pipe entirely, leaving it empty again. > > Finding it not just non-empty, but full means that something's very > wrong. The actor here is essentially ->splice_write(), and I'm really > curious which file is the target. Actually, could you turn those > WARN_ON() into > if (WARN_ON(pipe->nr_bufs)) > printk(KERN_ERR "->splice_write = %p", > sd->u.file->f_op->splice_write); > and see which function it is?
s/nr_bufs/nrbufs/ aside, I tried this, and it didn't trigger, even though I hit the iov_iter_pipe WARN again.
Dave
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