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Commit 87124e58 authored by Steven Whitehouse's avatar Steven Whitehouse
Browse files

[GFS2] Fix two races relating to glock callbacks 



One of the races relates to referencing a variable while not holding
its protecting spinlock. The patch simply moves the test inside the
spin lock. The other races occurs when a demote to unlocked request
occurs during the time a demote to shared request is already running.
This of course only happens in the case that the lock was in the
exclusive mode to start with. The patch adds a check to see if another
demote request has occurred in the mean time and if it has, then it
performs a second demote.

Signed-off-by: default avatarSteven Whitehouse <swhiteho@redhat.com>
parent bbf25010

fs/gfs2/glock.c

+18 −6
Original line number Diff line number Diff line
@@ -545,12 +545,14 @@ static int rq_demote(struct gfs2_glock *gl) 
		return 0;

	}

	set_bit(GLF_LOCK, &gl->gl_flags);

	spin_unlock(&gl->gl_spin);

	if (gl->gl_demote_state == LM_ST_UNLOCKED ||

	    gl->gl_state != LM_ST_EXCLUSIVE)

	    gl->gl_state != LM_ST_EXCLUSIVE) {

		spin_unlock(&gl->gl_spin);

		gfs2_glock_drop_th(gl);

	else

	} else {

		spin_unlock(&gl->gl_spin);

		gfs2_glock_xmote_th(gl, NULL);

	}

	spin_lock(&gl->gl_spin);



	return 0;
@@ -760,10 +762,20 @@ static void xmote_bh(struct gfs2_glock *gl, unsigned int ret) 


	if (!gh) {

		gl->gl_stamp = jiffies;

		if (ret & LM_OUT_CANCELED)

		if (ret & LM_OUT_CANCELED) {

			op_done = 0;

		else

		} else {

			spin_lock(&gl->gl_spin);

			if (gl->gl_state != gl->gl_demote_state) {

				gl->gl_req_bh = NULL;

				spin_unlock(&gl->gl_spin);

				gfs2_glock_drop_th(gl);

				gfs2_glock_put(gl);

				return;

			}

			gfs2_demote_wake(gl);

			spin_unlock(&gl->gl_spin);

		}

	} else {

		spin_lock(&gl->gl_spin);

		list_del_init(&gh->gh_list);
@@ -817,7 +829,7 @@ static void xmote_bh(struct gfs2_glock *gl, unsigned int ret) 
 *

 */



void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh)

static void gfs2_glock_xmote_th(struct gfs2_glock *gl, struct gfs2_holder *gh)

{

	struct gfs2_sbd *sdp = gl->gl_sbd;

	int flags = gh ? gh->gh_flags : 0;