Date: Sat, 13 Apr 2002 04:17:46 -0700 (PDT) From: David Schultz <dschultz@uclink.Berkeley.EDU> To: FreeBSD-gnats-submit@FreeBSD.org Subject: kern/37035: [PATCH] msdosfs_readdir() freezes after failed write Message-ID: <200204131117.g3DBHkR21118@HAL9000.wox.org>
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>Number: 37035
>Category: kern
>Synopsis: [PATCH] msdosfs_readdir() freezes after failed write
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sat Apr 13 04:20:01 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator: David Schultz
>Release: FreeBSD 4.5-RELEASE-p2 i386
>Organization:
>Environment:
Problem affects all versions of FreeBSD from at least 4.0-RELEASE.
to 5.0-CURRENT
>Description:
After an attempt to write a buffer to a write-protected or otherwise
bad floppy, attempts to bread() the same block return success, but the
resulting buffer has b_count == b_resid. Unlike the UFS code, which
correctly handles this situation, msdosfs_readdir() goes into an
infinite loop.
>How-To-Repeat:
Mount a write-protected DOS floppy, then...
/flp# cat > foo
(error)
/flp# ls
(lockup)
>Fix:
This patch causes msdosfs_readdir() to give up in the case where it would
otherwise spin forever. There is still room for improvement; for example,
the buffer cache ought to give up when the floppy is forcibly unmounted.
However, this solves the actual lockup that many people complain about.
Index: msdosfs_vnops.c
===================================================================
RCS file: /home/ncvs/src/sys/fs/msdosfs/msdosfs_vnops.c,v
retrieving revision 1.119
diff -u -r1.119 msdosfs_vnops.c
--- msdosfs_vnops.c 2002/04/05 14:01:04 1.119
+++ msdosfs_vnops.c 2002/04/12 23:12:27
@@ -1603,7 +1603,16 @@
brelse(bp);
return (error);
}
+
+ /*
+ * If a short read occurred, the buffer may contain
+ * less valid data than expected.
+ */
n = min(n, blsize - bp->b_resid);
+ if (n == 0) {
+ brelse(bp);
+ break;
+ }
/*
* Convert from dos directory entries to fs-independent
>Release-Note:
>Audit-Trail:
>Unformatted:
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