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fix long-standing XXX in getblk(): NFS does funky things (somewhat 

explained in comments), which can cause a race condition.  amazingly,
the _only_ time i've ever seen or heard of this problem was in some
comments and sources by Rick Macklem, and when running against the
a DEC OSF/1 NFS server running on an Alpha.
This commit is contained in:
cgd 1995-07-12 07:39:00 +00:00
parent eac9104365
commit 9c3fe30d92
1 changed files with 31 additions and 2 deletions
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33
sys/kern/vfs_bio.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vfs_bio.c,v 1.36 1995/06/20 10:42:33 cgd Exp $ */
/* $NetBSD: vfs_bio.c,v 1.37 1995/07/12 07:39:00 cgd Exp $ */
/*-
* Copyright (c) 1994 Christopher G. Demetriou
@ -269,6 +269,13 @@ bwrite(bp)
/* Remember buffer type, to switch on it later. */
sync = !ISSET(bp->b_flags, B_ASYNC);
#if 0
if (sync && bp->b_vp && bp->b_vp->v_mount &&
ISSET(bp->b_vp->v_mount->mnt_flag, MNT_ASYNC)) {
bdwrite(bp);
return (0);
}
#endif
wasdelayed = ISSET(bp->b_flags, B_DELWRI);
CLR(bp->b_flags, (B_READ | B_DONE | B_ERROR | B_DELWRI));
@ -498,7 +505,23 @@ getblk(vp, blkno, size, slpflag, slptimeo)
start:
s = splbio();
if (bp = incore(vp, blkno)) { /* XXX NFS VOP_BWRITE foolishness */
/*
* XXX
* The following is an inlined version of 'incore()', but with
* the 'invalid' test moved to after the 'busy' test. It's
* necessary because there are some cases in which the NFS
* code sets B_INVAL prior to writing data to the server, but
* in which the buffers actually contain valid data. In this
* case, we can't allow the system to allocate a new buffer for
* the block until the write is finished.
*/
loop:
bp = BUFHASH(vp, blkno)->lh_first;
for (; bp != NULL; bp = bp->b_hash.le_next) {
if (bp->b_lblkno != blkno || bp->b_vp != vp)
continue;
if (ISSET(bp->b_flags, B_BUSY)) {
SET(bp->b_flags, B_WANTED);
err = tsleep(bp, slpflag | (PRIBIO + 1), "getblk",
@ -508,6 +531,12 @@ start:
return (NULL);
goto start;
}
if (!ISSET(bp->b_flags, B_INVAL))
break;
}
if (bp) {
SET(bp->b_flags, (B_BUSY | B_CACHE));
bremfree(bp);
splx(s);