From: Wendy Cheng <wcheng@redhat.com> Subject: Re: [RHEL 5.2 PATCH] GFS2 - handle multiple demote requests Date: Fri, 05 Oct 2007 00:33:12 -0400 Bugzilla: 295641 Message-Id: <4705BE88.5000605@redhat.com> Changelog: [GFS2] handle multiple demote requests Make a correction based on Josef's comment on cluster-devel (bugzilla 295641) ..... Wendy Fix a race condition where multiple glock demote requests are sent to a node back-to-back. This patch does a check inside handle_callback() to see whether a demote request is in progress. If true, it sets a flag to make sure run_queue() will loop again to handle the new request, instead of erronously setting gl_demote_state to a different state. --- e48-brew/fs/gfs2/incore.h 2007-09-20 17:29:00.000000000 -0500 +++ e48/fs/gfs2/incore.h 2007-10-02 16:45:38.000000000 -0500 @@ -171,6 +171,7 @@ enum { GLF_DEMOTE = 3, GLF_PENDING_DEMOTE = 4, GLF_DIRTY = 5, + GLF_DEMOTE_IN_PROGRESS = 6, }; struct gfs2_glock { @@ -190,6 +191,7 @@ struct gfs2_glock { struct list_head gl_holders; struct list_head gl_waiters1; /* HIF_MUTEX */ struct list_head gl_waiters3; /* HIF_PROMOTE */ + int gl_waiters2; /* GIF_DEMOTE */ const struct gfs2_glock_operations *gl_ops; --- e48-brew/fs/gfs2/glock.c 2007-09-18 11:26:53.000000000 -0500 +++ e48/fs/gfs2/glock.c 2007-10-04 22:44:43.000000000 -0500 @@ -566,7 +566,10 @@ static int rq_demote(struct gfs2_glock * gfs2_demote_wake(gl); return 0; } + set_bit(GLF_LOCK, &gl->gl_flags); + set_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags); + if (gl->gl_demote_state == LM_ST_UNLOCKED || gl->gl_state != LM_ST_EXCLUSIVE) { spin_unlock(&gl->gl_spin); @@ -575,7 +578,9 @@ static int rq_demote(struct gfs2_glock * spin_unlock(&gl->gl_spin); gfs2_glock_xmote_th(gl, NULL); } + spin_lock(&gl->gl_spin); + clear_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags); return 0; } @@ -605,6 +610,11 @@ static void run_queue(struct gfs2_glock } else if (test_bit(GLF_DEMOTE, &gl->gl_flags)) { blocked = rq_demote(gl); + if (gl->gl_waiters2 && !blocked) { + set_bit(GLF_DEMOTE, &gl->gl_flags); + gl->gl_demote_state = LM_ST_UNLOCKED; + } + gl->gl_waiters2 = 0; } else if (!list_empty(&gl->gl_waiters3)) { gh = list_entry(gl->gl_waiters3.next, struct gfs2_holder, gh_list); @@ -721,7 +731,10 @@ static void handle_callback(struct gfs2_ } } else if (gl->gl_demote_state != LM_ST_UNLOCKED && gl->gl_demote_state != state) { - gl->gl_demote_state = LM_ST_UNLOCKED; + if (test_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags)) + gl->gl_waiters2 = 1; + else + gl->gl_demote_state = LM_ST_UNLOCKED; } spin_unlock(&gl->gl_spin); }