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Subject[PATCH 01/58] [GFS2] Handle multiple glock demote requests
Date
From: Wendy Cheng <wcheng@redhat.com>

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.

Signed-off-by: S. Wendy Cheng <wcheng@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a37efe4..104e83f 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -567,7 +567,10 @@ static int rq_demote(struct gfs2_glock *gl)
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);
@@ -576,7 +579,9 @@ static int rq_demote(struct gfs2_glock *gl)
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;
}
@@ -606,6 +611,11 @@ static void run_queue(struct gfs2_glock *gl)

} 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);
@@ -722,7 +732,10 @@ static void handle_callback(struct gfs2_glock *gl, unsigned int state,
}
} 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);
}
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index eaddfb5..662182b 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -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;

--
1.5.1.2


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