Date: Mon, 30 Jun 2003 04:55:35 -0700 From: David Schultz <das@FreeBSD.ORG> To: "Tim J. Robbins" <tjr@FreeBSD.ORG> Cc: cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/fs/msdosfs msdosfs_vfsops.c Message-ID: <20030630115535.GA586@HAL9000.homeunix.com> In-Reply-To: <200306290306.h5T360Ep009734@repoman.freebsd.org> References: <200306290306.h5T360Ep009734@repoman.freebsd.org>
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On Sat, Jun 28, 2003, Tim J. Robbins wrote:
> Fixes lockup when creating files on msdosfs mounts that have been
> mounted read-only then upgraded to read-write. The exact cause of
> the lockup is not known, but it is likely to be the kernel getting
> stuck in an infinite loop trying to write dirty buffers to a device
> without write permission.
If this is the problem I think it is, then not quite. After a
failed write, msdosfs_readdir() gets into an infinite loop because
bread() returns a buffer with a b_resid of 0. Partial fix:
Index: sys/fs/msdosfs/msdosfs_vnops.c
===================================================================
RCS file: /cvs/src/sys/fs/msdosfs/msdosfs_vnops.c,v
retrieving revision 1.138
diff -u -r1.138 msdosfs_vnops.c
--- sys/fs/msdosfs/msdosfs_vnops.c 15 Jun 2003 18:52:57 -0000 1.138
+++ sys/fs/msdosfs/msdosfs_vnops.c 30 Jun 2003 11:49:09 -0000
@@ -1571,6 +1571,10 @@
return (error);
}
n = min(n, blsize - bp->b_resid);
+ if (n == 0) {
+ brelse(bp);
+ return (EIO);
+ }
/*
* Convert from dos directory entries to fs-independent
I call this a partial fix because instead of locking up, readdir()
reports that the directory is empty, and I have't bothered to
track that part down. See also kern/37035.
There is a not-so-tight infinite loop for writing, where the
system tries to push the failed buffer out again every 5 seconds
or so, but that's really a separate issue, and a harder one to
solve (unless you believe phk ;-). There was a discussion about
it last October, in the thread ``Patch to allow a driver to report
unrecoverable write errors to the buf layer''.
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