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From: Steven Whitehouse on 2 Aug 2010 05:50
This is a clean up of the code which deals with LM_FLAG_NOEXP
which aims to remove any possible race conditions by using
gl_spin to cover the gap between testing for the LM_FLAG_NOEXP
and the GL_FROZEN flag.

Signed-off-by: Steven Whitehouse <swhiteho(a)redhat.com>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 2b3d8f8..9adf8f9 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1063,6 +1063,9 @@ int gfs2_glock_nq(struct gfs2_holder *gh)

spin_lock(&gl->gl_spin);
add_to_queue(gh);
+ if ((LM_FLAG_NOEXP & gh->gh_flags) &&
+ test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
+ set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
run_queue(gl, 1);
spin_unlock(&gl->gl_spin);

@@ -1320,6 +1323,36 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
}

/**
+ * gfs2_should_freeze - Figure out if glock should be frozen
+ * @gl: The glock in question
+ *
+ * Glocks are not frozen if (a) the result of the dlm operation is
+ * an error, (b) the locking operation was an unlock operation or
+ * (c) if there is a "noexp" flagged request anywhere in the queue
+ *
+ * Returns: 1 if freezing should occur, 0 otherwise
+ */
+
+static int gfs2_should_freeze(const struct gfs2_glock *gl)
+{
+ const struct gfs2_holder *gh;
+
+ if (gl->gl_reply & ~LM_OUT_ST_MASK)
+ return 0;
+ if (gl->gl_target == LM_ST_UNLOCKED)
+ return 0;
+
+ list_for_each_entry(gh, &gl->gl_holders, gh_list) {
+ if (test_bit(HIF_HOLDER, &gh->gh_iflags))
+ continue;
+ if (LM_FLAG_NOEXP & gh->gh_flags)
+ return 0;
+ }
+
+ return 1;
+}
+
+/**
* gfs2_glock_complete - Callback used by locking
* @gl: Pointer to the glock
* @ret: The return value from the dlm
@@ -1329,18 +1362,17 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
{
struct lm_lockstruct *ls = &gl->gl_sbd->sd_lockstruct;
+
gl->gl_reply = ret;
+
if (unlikely(test_bit(DFL_BLOCK_LOCKS, &ls->ls_flags))) {
- struct gfs2_holder *gh;
spin_lock(&gl->gl_spin);
- gh = find_first_waiter(gl);
- if ((!(gh && (gh->gh_flags & LM_FLAG_NOEXP)) &&
- (gl->gl_target != LM_ST_UNLOCKED)) ||
- ((ret & ~LM_OUT_ST_MASK) != 0))
+ if (gfs2_should_freeze(gl)) {
set_bit(GLF_FROZEN, &gl->gl_flags);
- spin_unlock(&gl->gl_spin);
- if (test_bit(GLF_FROZEN, &gl->gl_flags))
+ spin_unlock(&gl->gl_spin);
return;
+ }
+ spin_unlock(&gl->gl_spin);
}
set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
gfs2_glock_hold(gl);
--
1.7.1.1

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