PR/57659 CVS commit: src

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

The following reply was made to PR kern/57659; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/57659 CVS commit: src
Date: Sat, 3 Oct 2026 16:23:18 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Sat Oct  3 16:23:18 UTC 2026
 
 Modified Files:
 	src/sys/kern: sys_pipe.c
 	src/tests/kernel: t_fdrestart.c
 
 Log Message:
 pipe(2): Fix wakeup of pending writers on close of write side.
 
 The job of pipe_restart is to wake any pending I/O operations on the
 file when it is about to be closed.  New references cannot be taken
 for new I/O operations; once all existing references are drained, the
 system calls pipe_close.
 
 What pipe_restart did was to wake pipe->pipe_rcv and pipe->pipe_wcv.
 But the condvars of _which pipe_?
 
 After renaming the variables to match reality, it becomes clear that
 wpipe->pipe_wcv and wpipe->pipe_rcv are never used -- instead,
 pipe_read waits for rpipe->pipe_rcv, and pipe_write waits for
 rpipe->pipe_wcv.  So pipe_restart on the write side of a pipe woke
 wpipe->pipe_rcv and wpipe->pipe_wcv, which nothing was waiting for,
 and failed to wake rpipe->pipe_rcv or rpipe->pipe_wcv.
 
 (Perhaps we should just have a single struct pipe::pipe_cv member,
 and have pipe_read use rpipe->pipe_cv and pipe_write use
 wpipe->pipe_cv.  But that will be left for future cleanup.)
 
 PR kern/57659: closing pipe writefd fails to wake concurrent write on
 same writefd
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.170 -r1.171 src/sys/kern/sys_pipe.c
 cvs rdiff -u -r1.11 -r1.12 src/tests/kernel/t_fdrestart.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.