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Commit 901c6c66 authored by Bob Peterson's avatar Bob Peterson
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GFS2: Update master statfs buffer with sd_statfs_spin locked 



Before this patch, function update_statfs called gfs2_statfs_change_out
to update the master statfs buffer without the sd_statfs_spin held.
In theory, another process could call gfs2_statfs_sync, which takes
the sd_statfs_spin lock and re-reads m_sc from the buffer. So there's
a theoretical timing window in which one process could write the
master statfs buffer, then another comes along and re-reads it, wiping
out the changes.

Signed-off-by: default avatarBob Peterson <rpeterso@redhat.com>
parent b58bf407

fs/gfs2/super.c

+2 −3
Original line number Diff line number Diff line
@@ -556,6 +556,7 @@ void update_statfs(struct gfs2_sbd *sdp, struct buffer_head *m_bh, 
	struct gfs2_statfs_change_host *l_sc = &sdp->sd_statfs_local;



	gfs2_trans_add_meta(l_ip->i_gl, l_bh);

	gfs2_trans_add_meta(m_ip->i_gl, m_bh);



	spin_lock(&sdp->sd_statfs_spin);

	m_sc->sc_total += l_sc->sc_total;
@@ -564,10 +565,8 @@ void update_statfs(struct gfs2_sbd *sdp, struct buffer_head *m_bh, 
	memset(l_sc, 0, sizeof(struct gfs2_statfs_change));

	memset(l_bh->b_data + sizeof(struct gfs2_dinode),

	       0, sizeof(struct gfs2_statfs_change));

	spin_unlock(&sdp->sd_statfs_spin);



	gfs2_trans_add_meta(m_ip->i_gl, m_bh);

	gfs2_statfs_change_out(m_sc, m_bh->b_data + sizeof(struct gfs2_dinode));

	spin_unlock(&sdp->sd_statfs_spin);

}



int gfs2_statfs_sync(struct super_block *sb, int type)