From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bob Peterson Date: Tue, 6 Oct 2015 14:02:34 -0500 Subject: [Cluster-devel] [GFS2 PATCH v2 01/15] GFS2: Update master statfs buffer with sd_statfs_spin locked In-Reply-To: <1444158168-23036-1-git-send-email-rpeterso@redhat.com> References: <1444158168-23036-1-git-send-email-rpeterso@redhat.com> Message-ID: <1444158168-23036-2-git-send-email-rpeterso@redhat.com> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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 --- fs/gfs2/super.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c index 894fb01..a691725 100644 --- a/fs/gfs2/super.c +++ b/fs/gfs2/super.c @@ -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) -- 2.4.3