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rcu: Add full-sized polling for cond_sync_exp_full() 

The cond_synchronize_rcu_expedited() API compresses the combined expedited and
normal grace-period states into a single unsigned long, which conserves
storage, but can miss grace periods in certain cases involving overlapping
normal and expedited grace periods.  Missing the occasional grace period
is usually not a problem, but there are use cases that care about each
and every grace period.

This commit therefore adds yet another member of the full-state RCU
grace-period polling API, which is the cond_synchronize_rcu_exp_full()
function.  This uses up to three times the storage (rcu_gp_oldstate
structure instead of unsigned long), but is guaranteed not to miss
grace periods.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-08-04 15:23:26 -07:00
parent b6fe4917ae
commit 8df13f0160
4 changed files with 83 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/rcutiny.h
View File

@ -64,6 +64,11 @@ static inline void cond_synchronize_rcu_expedited(unsigned long oldstate)
cond_synchronize_rcu(oldstate);
}
static inline void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
{
cond_synchronize_rcu_expedited(rgosp->rgos_norm);
}
extern void rcu_barrier(void);
static inline void synchronize_rcu_expedited(void)

1
include/linux/rcutree.h
View File

@ -50,6 +50,7 @@ struct rcu_gp_oldstate {
unsigned long start_poll_synchronize_rcu_expedited(void);
void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
void cond_synchronize_rcu_expedited(unsigned long oldstate);
void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp);
unsigned long get_state_synchronize_rcu(void);
void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp);
unsigned long start_poll_synchronize_rcu(void);

72
kernel/rcu/rcutorture.c
View File

@ -85,6 +85,8 @@ torture_param(bool, fwd_progress_need_resched, 1, "Hide cond_resched() behind ne
torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives");
torture_param(bool, gp_cond_exp, false, "Use conditional/async expedited GP wait primitives");
torture_param(bool, gp_cond_full, false, "Use conditional/async full-state GP wait primitives");
torture_param(bool, gp_cond_exp_full, false,
"Use conditional/async full-stateexpedited GP wait primitives");
torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(bool, gp_normal, false, "Use normal (non-expedited) GP wait primitives");
torture_param(bool, gp_poll, false, "Use polling GP wait primitives");
@ -199,20 +201,22 @@ static int rcu_torture_writer_state;
#define RTWS_COND_GET 5
#define RTWS_COND_GET_FULL 6
#define RTWS_COND_GET_EXP 7
#define RTWS_COND_SYNC 8
#define RTWS_COND_SYNC_FULL 9
#define RTWS_COND_SYNC_EXP 10
#define RTWS_POLL_GET 11
#define RTWS_POLL_GET_FULL 12
#define RTWS_POLL_GET_EXP 13
#define RTWS_POLL_GET_EXP_FULL 14
#define RTWS_POLL_WAIT 15
#define RTWS_POLL_WAIT_FULL 16
#define RTWS_POLL_WAIT_EXP 17
#define RTWS_POLL_WAIT_EXP_FULL 18
#define RTWS_SYNC 19
#define RTWS_STUTTER 20
#define RTWS_STOPPING 21
#define RTWS_COND_GET_EXP_FULL 8
#define RTWS_COND_SYNC 9
#define RTWS_COND_SYNC_FULL 10
#define RTWS_COND_SYNC_EXP 11
#define RTWS_COND_SYNC_EXP_FULL 12
#define RTWS_POLL_GET 13
#define RTWS_POLL_GET_FULL 14
#define RTWS_POLL_GET_EXP 15
#define RTWS_POLL_GET_EXP_FULL 16
#define RTWS_POLL_WAIT 17
#define RTWS_POLL_WAIT_FULL 18
#define RTWS_POLL_WAIT_EXP 19
#define RTWS_POLL_WAIT_EXP_FULL 20
#define RTWS_SYNC 21
#define RTWS_STUTTER 22
#define RTWS_STOPPING 23
static const char * const rcu_torture_writer_state_names[] = {
"RTWS_FIXED_DELAY",
"RTWS_DELAY",
@ -222,9 +226,11 @@ static const char * const rcu_torture_writer_state_names[] = {
"RTWS_COND_GET",
"RTWS_COND_GET_FULL",
"RTWS_COND_GET_EXP",
"RTWS_COND_GET_EXP_FULL",
"RTWS_COND_SYNC",
"RTWS_COND_SYNC_FULL",
"RTWS_COND_SYNC_EXP",
"RTWS_COND_SYNC_EXP_FULL",
"RTWS_POLL_GET",
"RTWS_POLL_GET_FULL",
"RTWS_POLL_GET_EXP",
@ -350,6 +356,7 @@ struct rcu_torture_ops {
void (*start_gp_poll_exp_full)(struct rcu_gp_oldstate *rgosp);
bool (*poll_gp_state_exp)(unsigned long oldstate);
void (*cond_sync_exp)(unsigned long oldstate);
void (*cond_sync_exp_full)(struct rcu_gp_oldstate *rgosp);
unsigned long (*get_gp_state)(void);
void (*get_gp_state_full)(struct rcu_gp_oldstate *rgosp);
unsigned long (*get_gp_completed)(void);
@ -1183,16 +1190,17 @@ static int nsynctypes;
static void rcu_torture_write_types(void)
{
bool gp_cond1 = gp_cond, gp_cond_exp1 = gp_cond_exp, gp_cond_full1 = gp_cond_full;
bool gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp, gp_poll_exp_full1 = gp_poll_exp_full;
bool gp_normal1 = gp_normal, gp_poll1 = gp_poll, gp_poll_full1 = gp_poll_full;
bool gp_sync1 = gp_sync;
bool gp_cond_exp_full1 = gp_cond_exp_full, gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp;
bool gp_poll_exp_full1 = gp_poll_exp_full, gp_normal1 = gp_normal, gp_poll1 = gp_poll;
bool gp_poll_full1 = gp_poll_full, gp_sync1 = gp_sync;
/* Initialize synctype[] array. If none set, take default. */
if (!gp_cond1 && !gp_cond_exp1 && !gp_cond_full1 && !gp_exp1 && !gp_poll_exp &&
!gp_poll_exp_full1 && !gp_normal1 && !gp_poll1 && !gp_poll_full1 && !gp_sync1)
gp_cond1 = gp_cond_exp1 = gp_cond_full1 = gp_exp1 = gp_poll_exp1 =
gp_poll_exp_full1 = gp_normal1 = gp_poll1 = gp_poll_full1 =
gp_sync1 = true;
if (!gp_cond1 && !gp_cond_exp1 && !gp_cond_full1 && !gp_cond_exp_full1 && !gp_exp1 &&
!gp_poll_exp && !gp_poll_exp_full1 && !gp_normal1 && !gp_poll1 && !gp_poll_full1 &&
!gp_sync1)
gp_cond1 = gp_cond_exp1 = gp_cond_full1 = gp_cond_exp_full1 = gp_exp1 =
gp_poll_exp1 = gp_poll_exp_full1 = gp_normal1 = gp_poll1 =
gp_poll_full1 = gp_sync1 = true;
if (gp_cond1 && cur_ops->get_gp_state && cur_ops->cond_sync) {
synctype[nsynctypes++] = RTWS_COND_GET;
pr_info("%s: Testing conditional GPs.\n", __func__);
@ -1211,6 +1219,13 @@ static void rcu_torture_write_types(void)
} else if (gp_cond_full && (!cur_ops->get_gp_state || !cur_ops->cond_sync_full)) {
pr_alert("%s: gp_cond_full without primitives.\n", __func__);
}
if (gp_cond_exp_full1 && cur_ops->get_gp_state_exp && cur_ops->cond_sync_exp_full) {
synctype[nsynctypes++] = RTWS_COND_GET_EXP_FULL;
pr_info("%s: Testing conditional full-state expedited GPs.\n", __func__);
} else if (gp_cond_exp_full &&
(!cur_ops->get_gp_state_exp || !cur_ops->cond_sync_exp_full)) {
pr_alert("%s: gp_cond_exp_full without primitives.\n", __func__);
}
if (gp_exp1 && cur_ops->exp_sync) {
synctype[nsynctypes++] = RTWS_EXP_SYNC;
pr_info("%s: Testing expedited GPs.\n", __func__);
@ -1418,6 +1433,14 @@ rcu_torture_writer(void *arg)
cur_ops->cond_sync_full(&gp_snap_full);
rcu_torture_pipe_update(old_rp);
break;
case RTWS_COND_GET_EXP_FULL:
rcu_torture_writer_state = RTWS_COND_GET_EXP_FULL;
cur_ops->get_gp_state_full(&gp_snap_full);
torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
rcu_torture_writer_state = RTWS_COND_SYNC_EXP_FULL;
cur_ops->cond_sync_exp_full(&gp_snap_full);
rcu_torture_pipe_update(old_rp);
break;
case RTWS_POLL_GET:
rcu_torture_writer_state = RTWS_POLL_GET;
gp_snap = cur_ops->start_gp_poll();
@ -1567,6 +1590,11 @@ rcu_torture_fakewriter(void *arg)
torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
cur_ops->cond_sync_full(&gp_snap_full);
break;
case RTWS_COND_GET_EXP_FULL:
cur_ops->get_gp_state_full(&gp_snap_full);
torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand);
cur_ops->cond_sync_exp_full(&gp_snap_full);
break;
case RTWS_POLL_GET:
gp_snap = cur_ops->start_gp_poll();
while (!cur_ops->poll_gp_state(gp_snap)) {

27
kernel/rcu/tree_exp.h
View File

@ -1071,3 +1071,30 @@ void cond_synchronize_rcu_expedited(unsigned long oldstate)
synchronize_rcu_expedited();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
/**
* cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
* @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
*
* If a full RCU grace period has elapsed since the call to
* get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
* or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
* obtained, just return. Otherwise, invoke synchronize_rcu_expedited()
* to wait for a full grace period.
*
* Yes, this function does not take counter wrap into account.
* But counter wrap is harmless. If the counter wraps, we have waited for
* more than 2 billion grace periods (and way more on a 64-bit system!),
* so waiting for a couple of additional grace periods should be just fine.
*
* This function provides the same memory-ordering guarantees that
* would be provided by a synchronize_rcu() that was invoked at the call
* to the function that provided @rgosp and that returned at the end of
* this function.
*/
void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
{
if (!poll_state_synchronize_rcu_full(rgosp))
synchronize_rcu_expedited();
}
EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);