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GFS2: Update master statfs buffer with sd_statfs_spin locked

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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>
This commit is contained in:
Bob Peterson 2015-03-11 09:52:31 -05:00
parent b58bf407ca
commit 901c6c665b
1 changed files with 2 additions and 3 deletions
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5
fs/gfs2/super.c
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@ -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)