GFS2: Update master statfs buffer with sd_statfs_spin locked (901c6c66) · Commits · 戴 / test

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:

Bob Peterson <rpeterso@redhat.com>

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)

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