Commit 0befb851 authored by Bob Peterson's avatar Bob Peterson Committed by Andreas Gruenbacher
Browse files

gfs2: do_promote glock holder stealing fix 



In do_promote(), when the glock had no strong holders, we were
accidentally calling demote_incompat_holders() with new_gh == NULL, so
no weak holders were considered incompatible.  Instead, the new holder
should have been passed in.

For doing that, the HIF_HOLDER flag needs to be set in new_gh to prevent
may_grant() from complaining.  This means that the new holder will now
be recognized as a current holder, so skip over it explicitly in
demote_incompat_holders() to prevent it from being dequeued.

To further clarify things, we can now rename new_gh to current_gh in
demote_incompat_holders(); after all, the HIF_HOLDER flag is already set,
which means the new holder is already a current holder.

Signed-off-by: default avatarBob Peterson <rpeterso@redhat.com>
Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent 8f0028fc

fs/gfs2/glock.c

+12 −7
Original line number Diff line number Diff line
@@ -405,10 +405,13 @@ static void do_error(struct gfs2_glock *gl, const int ret) 
/**

 * demote_incompat_holders - demote incompatible demoteable holders

 * @gl: the glock we want to promote

 * @new_gh: the new holder to be promoted

 * @current_gh: the newly promoted holder

 *

 * We're passing the newly promoted holder in @current_gh, but actually, any of

 * the strong holders would do.

 */

static void demote_incompat_holders(struct gfs2_glock *gl,

				    struct gfs2_holder *new_gh)

				    struct gfs2_holder *current_gh)

{

	struct gfs2_holder *gh, *tmp;
@@ -424,8 +427,10 @@ static void demote_incompat_holders(struct gfs2_glock *gl, 
		 */

		if (!test_bit(HIF_HOLDER, &gh->gh_iflags))

			return;

		if (gh == current_gh)

			continue;

		if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags) &&

		    !may_grant(gl, new_gh, gh)) {

		    !may_grant(gl, current_gh, gh)) {

			/*

			 * We should not recurse into do_promote because

			 * __gfs2_glock_dq only calls handle_callback,
@@ -547,14 +552,14 @@ static int do_promote(struct gfs2_glock *gl) 
			do_error(gl, 0);

			break;

		}

		set_bit(HIF_HOLDER, &gh->gh_iflags);

		trace_gfs2_promote(gh);

		gfs2_holder_wake(gh);

		if (!incompat_holders_demoted) {

			current_gh = gh;

			demote_incompat_holders(gl, current_gh);

			incompat_holders_demoted = true;

			current_gh = gh;

		}

		set_bit(HIF_HOLDER, &gh->gh_iflags);

		trace_gfs2_promote(gh);

		gfs2_holder_wake(gh);

	}

	return 0;

}