Commit b6900ce1 authored by Andreas Gruenbacher's avatar Andreas Gruenbacher
Browse files

gfs2: Simplify DLM_LKF_QUECVT use 



The DLM_LKF_QUECVT flag needs to be set for "upward" lock conversions to
ensure fairness, but setting it for "downward" lock conversions will
lead to a failure.  The flag is currently set based on the GLF_BLOCKING
flag and it's not immediately obvious why this is correct.  Simplify
things by figuring out if a lock conversion is "upward" by looking at
the before and after locking modes instead of relying on the
GLF_BLOCKING flag.

Signed-off-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
parent 03ff3781

fs/gfs2/lock_dlm.c

+25 −4
Original line number Diff line number Diff line
@@ -224,8 +224,21 @@ static int make_mode(struct gfs2_sbd *sdp, const unsigned int lmstate) 
	return -1;

}



/* Taken from fs/dlm/lock.c. */



static bool middle_conversion(int cur, int req)

{

	return (cur == DLM_LOCK_PR && req == DLM_LOCK_CW) ||

	       (cur == DLM_LOCK_CW && req == DLM_LOCK_PR);

}



static bool down_conversion(int cur, int req)

{

	return !middle_conversion(cur, req) && req < cur;

}



static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags,

		      const int req)

		      const int cur, const int req)

{

	u32 lkf = 0;
@@ -251,7 +264,14 @@ static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags, 


	if (!test_bit(GLF_INITIAL, &gl->gl_flags)) {

		lkf |= DLM_LKF_CONVERT;

		if (test_bit(GLF_BLOCKING, &gl->gl_flags))



		/*

		 * The DLM_LKF_QUECVT flag needs to be set for "first come,

		 * first served" semantics, but it must only be set for

		 * "upward" lock conversions or else DLM will reject the

		 * request as invalid.

		 */

		if (!down_conversion(cur, req))

			lkf |= DLM_LKF_QUECVT;

	}
@@ -271,13 +291,14 @@ static int gdlm_lock(struct gfs2_glock *gl, unsigned int req_state, 
		     unsigned int flags)

{

	struct lm_lockstruct *ls = &gl->gl_name.ln_sbd->sd_lockstruct;

	int req;

	int cur, req;

	u32 lkf;

	char strname[GDLM_STRNAME_BYTES] = "";

	int error;



	cur = make_mode(gl->gl_name.ln_sbd, gl->gl_state);

	req = make_mode(gl->gl_name.ln_sbd, req_state);

	lkf = make_flags(gl, flags, req);

	lkf = make_flags(gl, flags, cur, req);

	gfs2_glstats_inc(gl, GFS2_LKS_DCOUNT);

	gfs2_sbstats_inc(gl, GFS2_LKS_DCOUNT);

	if (test_bit(GLF_INITIAL, &gl->gl_flags)) {