CVS commit: src/sys/kern

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Sat Oct  3 16:23:46 UTC 2026

Modified Files:
        src/sys/kern: sys_pipe.c

Log Message:
pipe(2): Make pipe sides a little more symmetric.

1. When reading from or writing to a pipe, busy _this side_ of the
   pipe, not the other side.

2. In pipeclose, all operations on _this side_ of the pipe have already
   quiesced.  But operations on the other side may not have.  So wait
   for the _other side_ to be unbusied before disconnecting the peer
   (changing ppipe->pipe_peer from pipe to NULL).

With (1) and (2) we can prove a simple property that makes reasoning
about this code easier: If a pipe is busy, its peer pointer is stable
even across cv_wait on the pipe lock.  Without these changes I'm not
sure I could prove that property (though I haven't exhibited a
reproducer for any issues arising from its failure).

3. Make write wait on wpipe->pipe_wcv, and make read wait on
   rpipe->pipe_rcv, consistently, so that any waiters on one side of a
   pipe will always be waiting on one of _that side's_ condvars.

   This makes the logic in pipe_restart to wake any pending operations
   on _this side_ simpler -- it doesn't have to reach over to the peer,
   and it doesn't have to inadvertently wake the peer for no reason.

   In fact this brings the text of the code in pipe_restart back to
   what it was before I renamed the variables to reflect their actual
   content, suggesting there has been some confusion from the variable
   naming over the years...

   (In a future change, I would like to merge pipe_rcv and pipe_wcv
   into a single condvar per side -- no need to initialize two extra
   condvars per pipe that will never be used!)

Preparation for:

PR kern/59056: poll POLLHUP bugs


To generate a diff of this commit:
cvs rdiff -u -r1.171 -r1.172 src/sys/kern/sys_pipe.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.