From: Mathieu Desnoyers Date: Mon, 11 May 2009 20:58:17 +0000 (-0400) Subject: Add Paul's URCU model X-Git-Tag: v0.1~237 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=3162dfe1928d4d6bf857f8e9e1c814eb8a994a0d;p=urcu.git Add Paul's URCU model Signed-off-by: Mathieu Desnoyers --- diff --git a/formal-model/urcu-paulmck/urcu-paulmck.spin b/formal-model/urcu-paulmck/urcu-paulmck.spin new file mode 100644 index 0000000..e20a6e5 --- /dev/null +++ b/formal-model/urcu-paulmck/urcu-paulmck.spin @@ -0,0 +1,299 @@ +/* + * urcu_mbmin.spin: Promela code to validate urcu. See commit number + * 3a9e6e9df706b8d39af94d2f027210e2e7d4106e of Mathieu Desnoyer's + * git archive at git://lttng.org/userspace-rcu.git, but with + * memory barriers removed. + * + * 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 && + reader_progress[0] == reader_progress[3] -> + done = 1; + break; + :: tmp >= 4 && + reader_progress[0] != reader_progress[3] -> + 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() +{ + byte tmp; + + /* prior synchronize_rcu(), second counter flip. */ + need_mb = 1; /* mb() A */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; + need_mb = 1; /* mb() B */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + do + :: 1 -> + 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; /* mb() C absolutely required by analogy with G */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + + /* Removal statement, e.g., list_del_rcu(). */ + removed = 1; + + /* current synchronize_rcu(), first counter flip. */ + need_mb = 1; /* mb() D suggested */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; + need_mb = 1; /* mb() E required if D not present */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + + /* current synchronize_rcu(), first-flip check plus second flip. */ + if + :: 1 -> + do + :: 1 -> + 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; + urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; + :: 1 -> + tmp = urcu_gp_ctr; + urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; + do + :: 1 -> + if + :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && + (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != + (tmp & ~RCU_GP_CTR_NEST_MASK) -> + skip; + :: else -> break; + fi; + od; + fi; + + /* current synchronize_rcu(), second counter flip check. */ + need_mb = 1; /* mb() F not required */ + do + :: need_mb == 1 -> skip; + :: need_mb == 0 -> break; + od; + do + :: 1 -> + 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; /* mb() G absolutely required */ + 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(); + } +} diff --git a/formal-model/urcu-paulmck/urcu.sh b/formal-model/urcu-paulmck/urcu.sh new file mode 100644 index 0000000..8ef0e87 --- /dev/null +++ b/formal-model/urcu-paulmck/urcu.sh @@ -0,0 +1,3 @@ +spin -a urcu-paulmck.spin +cc -DSAFETY -o pan pan.c +./pan