lkml.org 
[lkml]   [2009]   [Feb]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [ltt-dev] [RFC git tree] Userspace RCU (urcu) for Linux (repost)
    On Wed, Feb 11, 2009 at 11:08:24PM -0500, Mathieu Desnoyers wrote:
    > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:
    > > On Wed, Feb 11, 2009 at 04:35:49PM -0800, Paul E. McKenney wrote:
    > > > On Wed, Feb 11, 2009 at 04:42:58PM -0500, Mathieu Desnoyers wrote:
    > > > > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote:

    [ . . . ]

    > > And I had bugs in my model that allowed the rcu_read_lock() model
    > > to nest indefinitely, which overflowed into the top bit, messing
    > > things up. :-/
    > >
    > > Attached is a fixed model. This model validates correctly (woo-hoo!).
    > > Even better, gives the expected error if you comment out line 180 and
    > > uncomment line 213, this latter corresponding to the error case I called
    > > out a few days ago.
    > >
    >
    > Great ! :) I added this version to the git repository, hopefully it's ok
    > with you ?

    Works for me!

    > > I will play with removing models of mb...
    > >
    >
    > OK, I see you already did..

    I continued this, and surprisingly few are actually required, though
    I don't fully trust the modeling of removed memory barriers.

    Thanx, Paul

    > Mathieu
    >
    > > Thanx, Paul
    >
    > Content-Description: urcu.spin
    > > /*
    > > * urcu.spin: Promela code to validate urcu. See commit number
    > > * 3a9e6e9df706b8d39af94d2f027210e2e7d4106e of Mathieu Desnoyer's
    > > * git archive at git://lttng.org/userspace-rcu.git
    > > *
    > > * This program is free software; you can redistribute it and/or modify
    > > * it under the terms of the GNU General Public License as published by
    > > * the Free Software Foundation; either version 2 of the License, or
    > > * (at your option) any later version.
    > > *
    > > * This program is distributed in the hope that it will be useful,
    > > * but WITHOUT ANY WARRANTY; without even the implied warranty of
    > > * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    > > * GNU General Public License for more details.
    > > *
    > > * You should have received a copy of the GNU General Public License
    > > * along with this program; if not, write to the Free Software
    > > * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
    > > *
    > > * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
    > > */
    > >
    > > /* Promela validation variables. */
    > >
    > > bit removed = 0; /* Has RCU removal happened, e.g., list_del_rcu()? */
    > > bit free = 0; /* Has RCU reclamation happened, e.g., kfree()? */
    > > bit need_mb = 0; /* =1 says need reader mb, =0 for reader response. */
    > > byte reader_progress[4];
    > > /* Count of read-side statement executions. */
    > >
    > > /* urcu definitions and variables, taken straight from the algorithm. */
    > >
    > > #define RCU_GP_CTR_BIT (1 << 7)
    > > #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
    > >
    > > byte urcu_gp_ctr = 1;
    > > byte urcu_active_readers = 0;
    > >
    > > /* Model the RCU read-side critical section. */
    > >
    > > proctype urcu_reader()
    > > {
    > > bit done = 0;
    > > bit mbok;
    > > byte tmp;
    > > byte tmp_removed;
    > > byte tmp_free;
    > >
    > > /* Absorb any early requests for memory barriers. */
    > > do
    > > :: need_mb == 1 ->
    > > need_mb = 0;
    > > :: 1 -> skip;
    > > :: 1 -> break;
    > > od;
    > >
    > > /*
    > > * Each pass through this loop executes one read-side statement
    > > * from the following code fragment:
    > > *
    > > * rcu_read_lock(); [0a]
    > > * rcu_read_lock(); [0b]
    > > * p = rcu_dereference(global_p); [1]
    > > * x = p->data; [2]
    > > * rcu_read_unlock(); [3b]
    > > * rcu_read_unlock(); [3a]
    > > *
    > > * Because we are modeling a weak-memory machine, these statements
    > > * can be seen in any order, the only restriction being that
    > > * rcu_read_unlock() cannot precede the corresponding rcu_read_lock().
    > > * The placement of the inner rcu_read_lock() and rcu_read_unlock()
    > > * is non-deterministic, the above is but one possible placement.
    > > * Intestingly enough, this model validates all possible placements
    > > * of the inner rcu_read_lock() and rcu_read_unlock() statements,
    > > * with the only constraint being that the rcu_read_lock() must
    > > * precede the rcu_read_unlock().
    > > *
    > > * We also respond to memory-barrier requests, but only if our
    > > * execution happens to be ordered. If the current state is
    > > * misordered, we ignore memory-barrier requests.
    > > */
    > > do
    > > :: 1 ->
    > > if
    > > :: reader_progress[0] < 2 -> /* [0a and 0b] */
    > > tmp = urcu_active_readers;
    > > if
    > > :: (tmp & RCU_GP_CTR_NEST_MASK) == 0 ->
    > > tmp = urcu_gp_ctr;
    > > do
    > > :: (reader_progress[1] +
    > > reader_progress[2] +
    > > reader_progress[3] == 0) && need_mb == 1 ->
    > > need_mb = 0;
    > > :: 1 -> skip;
    > > :: 1 -> break;
    > > od;
    > > urcu_active_readers = tmp;
    > > :: else ->
    > > urcu_active_readers = tmp + 1;
    > > fi;
    > > reader_progress[0] = reader_progress[0] + 1;
    > > :: reader_progress[1] == 0 -> /* [1] */
    > > tmp_removed = removed;
    > > reader_progress[1] = 1;
    > > :: reader_progress[2] == 0 -> /* [2] */
    > > tmp_free = free;
    > > reader_progress[2] = 1;
    > > :: ((reader_progress[0] > reader_progress[3]) &&
    > > (reader_progress[3] < 2)) -> /* [3a and 3b] */
    > > tmp = urcu_active_readers - 1;
    > > urcu_active_readers = tmp;
    > > reader_progress[3] = reader_progress[3] + 1;
    > > :: else -> break;
    > > fi;
    > >
    > > /* Process memory-barrier requests, if it is safe to do so. */
    > > atomic {
    > > mbok = 0;
    > > tmp = 0;
    > > do
    > > :: tmp < 4 && reader_progress[tmp] == 0 ->
    > > tmp = tmp + 1;
    > > break;
    > > :: tmp < 4 && reader_progress[tmp] != 0 ->
    > > tmp = tmp + 1;
    > > :: tmp >= 4 ->
    > > done = 1;
    > > break;
    > > od;
    > > do
    > > :: tmp < 4 && reader_progress[tmp] == 0 ->
    > > tmp = tmp + 1;
    > > :: tmp < 4 && reader_progress[tmp] != 0 ->
    > > break;
    > > :: tmp >= 4 ->
    > > mbok = 1;
    > > break;
    > > od
    > >
    > > }
    > >
    > > if
    > > :: mbok == 1 ->
    > > /* We get here if mb processing is safe. */
    > > do
    > > :: need_mb == 1 ->
    > > need_mb = 0;
    > > :: 1 -> skip;
    > > :: 1 -> break;
    > > od;
    > > :: else -> skip;
    > > fi;
    > >
    > > /*
    > > * Check to see if we have modeled the entire RCU read-side
    > > * critical section, and leave if so.
    > > */
    > > if
    > > :: done == 1 -> break;
    > > :: else -> skip;
    > > fi
    > > od;
    > > assert((tmp_free == 0) || (tmp_removed == 1));
    > >
    > > /* Process any late-arriving memory-barrier requests. */
    > > do
    > > :: need_mb == 1 ->
    > > need_mb = 0;
    > > :: 1 -> skip;
    > > :: 1 -> break;
    > > od;
    > > }
    > >
    > > /* Model the RCU update process. */
    > >
    > > proctype urcu_updater()
    > > {
    > > /* Removal statement, e.g., list_del_rcu(). */
    > > removed = 1;
    > >
    > > /* synchronize_rcu(), first counter flip. */
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > > urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > > do
    > > :: 1 ->
    > > printf("urcu_gp_ctr=%x urcu_active_readers=%x\n", urcu_gp_ctr, urcu_active_readers);
    > > printf("urcu_gp_ctr&0x7f=%x urcu_active_readers&0x7f=%x\n", urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK, urcu_active_readers & ~RCU_GP_CTR_NEST_MASK);
    > > if
    > > :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 &&
    > > (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) !=
    > > (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) ->
    > > skip;
    > > :: else -> break;
    > > fi
    > > od;
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > >
    > > /* Erroneous removal statement, e.g., list_del_rcu(). */
    > > /* removed = 1; */
    > >
    > > /* synchronize_rcu(), second counter flip. */
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > > urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > > do
    > > :: 1 ->
    > > printf("urcu_gp_ctr=%x urcu_active_readers=%x\n", urcu_gp_ctr, urcu_active_readers);
    > > printf("urcu_gp_ctr&0x7f=%x urcu_active_readers&0x7f=%x\n", urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK, urcu_active_readers & ~RCU_GP_CTR_NEST_MASK);
    > > if
    > > :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 &&
    > > (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) !=
    > > (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) ->
    > > skip;
    > > :: else -> break;
    > > fi;
    > > od;
    > > need_mb = 1;
    > > do
    > > :: need_mb == 1 -> skip;
    > > :: need_mb == 0 -> break;
    > > od;
    > >
    > > /* free-up step, e.g., kfree(). */
    > > free = 1;
    > > }
    > >
    > > /*
    > > * Initialize the array, spawn a reader and an updater. Because readers
    > > * are independent of each other, only one reader is needed.
    > > */
    > >
    > > init {
    > > atomic {
    > > reader_progress[0] = 0;
    > > reader_progress[1] = 0;
    > > reader_progress[2] = 0;
    > > reader_progress[3] = 0;
    > > run urcu_reader();
    > > run urcu_updater();
    > > }
    > > }
    >
    >
    > --
    > Mathieu Desnoyers
    > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


    \
     
     \ /
      Last update: 2009-02-12 06:13    [W:0.046 / U:0.824 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site