Re: [PATCH 2/2] xfs: fix getbmap vs mmap deadlock

[Christoph Hellwig <hch@infradead.org>]

ping^2?

On Mon, Mar 16, 2009 at 02:30:57AM -0400, Christoph Hellwig wrote:
> ping?
> 
> On Tue, Feb 24, 2009 at 08:39:02AM -0500, Christoph Hellwig wrote:
> > xfs_getbmap (or rather the formatters called by it) copy out the getbmap
> > structures under the ilock, which can deadlock against mmap.  This has
> > been reported via bugzilla a while ago (#717) and has recently also
> > shown up via lockdep.
> > 
> > So allocate a temporary buffer to format the kernel getbmap structures
> > into and then copy them out after dropping the locks.
> > 
> > A little problem with this is that we limit the number of extents we
> > can copy out by the maximum allocation size, but I see no real way
> > around that.
> > 
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > 
> > Index: xfs/fs/xfs/xfs_bmap.c
> > ===================================================================
> > --- xfs.orig/fs/xfs/xfs_bmap.c	2009-02-23 20:38:27.512925014 +0100
> > +++ xfs/fs/xfs/xfs_bmap.c	2009-02-23 20:40:46.720926193 +0100
> > @@ -5867,12 +5867,13 @@ xfs_getbmap(
> >  	int			nexleft;	/* # of user extents left */
> >  	int			subnex;		/* # of bmapi's can do */
> >  	int			nmap;		/* number of map entries */
> > -	struct getbmapx		out;		/* output structure */
> > +	struct getbmapx		*out;		/* output structure */
> >  	int			whichfork;	/* data or attr fork */
> >  	int			prealloced;	/* this is a file with
> >  						 * preallocated data space */
> >  	int			iflags;		/* interface flags */
> >  	int			bmapi_flags;	/* flags for xfs_bmapi */
> > +	int			cur_ext = 0;
> >  
> >  	mp = ip->i_mount;
> >  	iflags = bmv->bmv_iflags;
> > @@ -5948,6 +5949,13 @@ xfs_getbmap(
> >  		return XFS_ERROR(EINVAL);
> >  	bmvend = bmv->bmv_offset + bmv->bmv_length;
> >  
> > +
> > +	if (bmv->bmv_count > ULONG_MAX / sizeof(struct getbmapx))
> > +		return XFS_ERROR(ENOMEM);
> > +	out = kmem_zalloc(bmv->bmv_count * sizeof(struct getbmapx), KM_MAYFAIL);
> > +	if (!out)
> > +		return XFS_ERROR(ENOMEM);
> > +
> >  	xfs_ilock(ip, XFS_IOLOCK_SHARED);
> >  	if (whichfork == XFS_DATA_FORK && !(iflags & BMV_IF_DELALLOC)) {
> >  		if (ip->i_delayed_blks || ip->i_size > ip->i_d.di_size) {
> > @@ -6001,39 +6009,39 @@ xfs_getbmap(
> >  		ASSERT(nmap <= subnex);
> >  
> >  		for (i = 0; i < nmap && nexleft && bmv->bmv_length; i++) {
> > -			int full = 0;	/* user array is full */
> > -
> > -			out.bmv_oflags = 0;
> > +			out[cur_ext].bmv_oflags = 0;
> >  			if (map[i].br_state == XFS_EXT_UNWRITTEN)
> > -				out.bmv_oflags |= BMV_OF_PREALLOC;
> > +				out[cur_ext].bmv_oflags |= BMV_OF_PREALLOC;
> >  			else if (map[i].br_startblock == DELAYSTARTBLOCK)
> > -				out.bmv_oflags |= BMV_OF_DELALLOC;
> > -			out.bmv_offset = XFS_FSB_TO_BB(mp, map[i].br_startoff);
> > -			out.bmv_length = XFS_FSB_TO_BB(mp, map[i].br_blockcount);
> > -			out.bmv_unused1 = out.bmv_unused2 = 0;
> > +				out[cur_ext].bmv_oflags |= BMV_OF_DELALLOC;
> > +			out[cur_ext].bmv_offset =
> > +				XFS_FSB_TO_BB(mp, map[i].br_startoff);
> > +			out[cur_ext].bmv_length =
> > +				XFS_FSB_TO_BB(mp, map[i].br_blockcount);
> > +			out[cur_ext].bmv_unused1 = 0;
> > +			out[cur_ext].bmv_unused2 = 0;
> >  			ASSERT(((iflags & BMV_IF_DELALLOC) != 0) ||
> >  			      (map[i].br_startblock != DELAYSTARTBLOCK));
> >                          if (map[i].br_startblock == HOLESTARTBLOCK &&
> >  			    whichfork == XFS_ATTR_FORK) {
> >  				/* came to the end of attribute fork */
> > -				out.bmv_oflags |= BMV_OF_LAST;
> > +				out[cur_ext].bmv_oflags |= BMV_OF_LAST;
> >  				goto out_free_map;
> >  			}
> >  
> > -			if (!xfs_getbmapx_fix_eof_hole(ip, &out, prealloced,
> > -					bmvend, map[i].br_startblock))
> > +			if (!xfs_getbmapx_fix_eof_hole(ip, &out[cur_ext],
> > +					prealloced, bmvend,
> > +					map[i].br_startblock))
> >  				goto out_free_map;
> >  
> > -			/* format results & advance arg */
> > -			error = formatter(&arg, &out, &full);
> > -			if (error || full)
> > -				goto out_free_map;
> >  			nexleft--;
> >  			bmv->bmv_offset =
> > -				out.bmv_offset + out.bmv_length;
> > +				out[cur_ext].bmv_offset +
> > +				out[cur_ext].bmv_length;
> >  			bmv->bmv_length =
> >  				max_t(__int64_t, 0, bmvend - bmv->bmv_offset);
> >  			bmv->bmv_entries++;
> > +			cur_ext++;
> >  		}
> >  	} while (nmap && nexleft && bmv->bmv_length);
> >  
> > @@ -6043,6 +6051,16 @@ xfs_getbmap(
> >  	xfs_iunlock_map_shared(ip, lock);
> >   out_unlock_iolock:
> >  	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
> > +
> > +	for (i = 0; i < cur_ext; i++) {
> > +		int full = 0;	/* user array is full */
> > +
> > +		/* format results & advance arg */
> > +		error = formatter(&arg, &out[i], &full);
> > +		if (error || full)
> > +			break;
> > +	}
> > +
> >  	return error;
> >  }
> >  
> > 
> > _______________________________________________
> > xfs mailing list
> > xfs@oss.sgi.com
> > http://oss.sgi.com/mailman/listinfo/xfs
> ---end quoted text---
> 
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