Re: bin/56422: zgrep -l sometimes hangs

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

The following reply was made to PR bin/56422; it has been noted by GNATS.

From: "J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>
To: NetBSD GNATS <gnats-bugs%netbsd.org@localhost>
Cc: 
Subject: Re: bin/56422: zgrep -l sometimes hangs
Date: Fri, 1 Oct 2021 10:24:35 +0200

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 This deadlock happens whenever the writer has more data and no space
 while the reader is closing the pipe.
 
 Simply swapping the EOF test and the wait_sig in pipe_write() should
 fix it.  Diff attached, please give it a try.
 
 --
 J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig (Germany)
 
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 pipe_stall
 
 Fix a deadlock where one thread writes to a pipe, has more data
 and no space in the pipe and waits on "pipe_wcv" while the reader
 is closing the pipe and waits on "pipe_draincv".
 
 Swap the test for "PIPE_EOF" and the "cv_wait_sig()" in "pipe_write()".
 
 PR bin/56422 "zgrep -l sometimes hangs"
 
 diff -r c0d659b6a82c -r 4b3d02a50e12 sys/kern/sys_pipe.c
 --- sys/kern/sys_pipe.c
 +++ sys/kern/sys_pipe.c
 @@ -694,11 +694,6 @@ pipe_write(file_t *fp, off_t *offset, st
  				break;
  			}
  
 -			pipeunlock(wpipe);
 -			error = cv_wait_sig(&wpipe->pipe_wcv, lock);
 -			(void)pipelock(wpipe, false);
 -			if (error != 0)
 -				break;
  			/*
  			 * If read side wants to go away, we just issue a signal
  			 * to ourselves.
 @@ -707,6 +702,12 @@ pipe_write(file_t *fp, off_t *offset, st
  				error = EPIPE;
  				break;
  			}
 +
 +			pipeunlock(wpipe);
 +			error = cv_wait_sig(&wpipe->pipe_wcv, lock);
 +			(void)pipelock(wpipe, false);
 +			if (error != 0)
 +				break;
  			wakeup_state = wpipe->pipe_state;
  		}
  	}
 
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