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Fix from Ethan Solomita <ethan@geocast.com> to avoid a livelock problem 

where the buffer cache code would be recycling B_AGE buffers with
dependencies.
This commit is contained in:
fvdl 2000-04-12 11:33:43 +00:00
parent c24f5b5068
commit ea3e5a38b8
1 changed files with 18 additions and 5 deletions
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23
sys/kern/vfs_bio.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: vfs_bio.c,v 1.66 2000/03/30 09:27:14 augustss Exp $ */
/* $NetBSD: vfs_bio.c,v 1.67 2000/04/12 11:33:43 fvdl Exp $ */
/*-
* Copyright (c) 1994 Christopher G. Demetriou
@ -573,16 +573,29 @@ brelse(bp)
/*
* It has valid data. Put it on the end of the appropriate
* queue, so that it'll stick around for as long as possible.
* If buf is AGE, but has dependencies, must put it on last
* bufqueue to be scanned, ie LRU. This protects against the
* livelock where BQ_AGE only has buffers with dependencies,
* and we thus never get to the dependent buffers in BQ_LRU.
*/
if (ISSET(bp->b_flags, B_LOCKED))
/* locked in core */
bufq = &bufqueues[BQ_LOCKED];
else if (ISSET(bp->b_flags, B_AGE))
/* stale but valid data */
bufq = &bufqueues[BQ_AGE];
else
else if (!ISSET(bp->b_flags, B_AGE))
/* valid data */
bufq = &bufqueues[BQ_LRU];
else {
/* stale but valid data */
int has_deps;
if (LIST_FIRST(&bp->b_dep) != NULL &&
bioops.io_countdeps)
has_deps = (*bioops.io_countdeps)(bp, 0);
else
has_deps = 0;
bufq = has_deps ? &bufqueues[BQ_LRU] :
&bufqueues[BQ_AGE];
}
binstailfree(bp, bufq);
}