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Prevent race condition where two threads can defer a buffer.

This commit is contained in:
mlelstv 2015-08-28 05:49:31 +00:00
parent 50408f97eb
commit 432d09fb65
2 changed files with 10 additions and 3 deletions
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10
sys/dev/dksubr.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: dksubr.c,v 1.74 2015/08/27 05:51:50 mlelstv Exp $ */
/* $NetBSD: dksubr.c,v 1.75 2015/08/28 05:49:31 mlelstv Exp $ */
/*-
* Copyright (c) 1996, 1997, 1998, 1999, 2002, 2008 The NetBSD Foundation, Inc.
@ -30,7 +30,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: dksubr.c,v 1.74 2015/08/27 05:51:50 mlelstv Exp $");
__KERNEL_RCSID(0, "$NetBSD: dksubr.c,v 1.75 2015/08/28 05:49:31 mlelstv Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@ -301,6 +301,10 @@ dk_start(struct dk_softc *dksc, struct buf *bp)
if (bp != NULL)
bufq_put(dksc->sc_bufq, bp);
if (dksc->sc_busy)
goto done;
dksc->sc_busy = true;
/*
* Peeking at the buffer queue and committing the operation
* only after success isn't atomic.
@ -339,6 +343,8 @@ dk_start(struct dk_softc *dksc, struct buf *bp)
bp = bufq_get(dksc->sc_bufq);
}
dksc->sc_busy = false;
done:
mutex_exit(&dksc->sc_iolock);
}

3
sys/dev/dkvar.h
View File

@ -1,4 +1,4 @@
/* $NetBSD: dkvar.h,v 1.22 2015/08/27 05:51:50 mlelstv Exp $ */
/* $NetBSD: dkvar.h,v 1.23 2015/08/28 05:49:31 mlelstv Exp $ */
/*-
* Copyright (c) 2002 The NetBSD Foundation, Inc.
@ -48,6 +48,7 @@ struct dk_softc {
struct bufq_state *sc_bufq; /* buffer queue */
int sc_dtype; /* disk type */
struct buf *sc_deferred; /* retry after start failed */
bool sc_busy; /* processing buffers */
};
/* sc_flags: