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    Subject[PATCH tip/core/rcu 06/13] rcu_sync: Simplify rcu_sync using new rcu_sync_ops structure
    Date
    From: Oleg Nesterov <oleg@redhat.com>

    This commit adds the new struct rcu_sync_ops which holds sync/call
    methods, and turns the function pointers in rcu_sync_struct into an array
    of struct rcu_sync_ops. This simplifies the "init" helpers by collapsing
    a switch statement and explicit multiple definitions into a simple
    assignment and a helper macro, respectively.

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    include/linux/rcu_sync.h | 60 +++++++++++++++++++-----------------------------
    kernel/rcu/sync.c | 42 +++++++++++++++++----------------
    2 files changed, 45 insertions(+), 57 deletions(-)

    diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
    index cb044df2e21c..c6d2272c4459 100644
    --- a/include/linux/rcu_sync.h
    +++ b/include/linux/rcu_sync.h
    @@ -26,6 +26,8 @@
    #include <linux/wait.h>
    #include <linux/rcupdate.h>

    +enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
    +
    /* Structure to mediate between updaters and fastpath-using readers. */
    struct rcu_sync {
    int gp_state;
    @@ -35,43 +37,9 @@ struct rcu_sync {
    int cb_state;
    struct rcu_head cb_head;

    - void (*sync)(void);
    - void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
    + enum rcu_sync_type gp_type;
    };

    -#define ___RCU_SYNC_INIT(name) \
    - .gp_state = 0, \
    - .gp_count = 0, \
    - .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
    - .cb_state = 0
    -
    -#define __RCU_SCHED_SYNC_INIT(name) { \
    - ___RCU_SYNC_INIT(name), \
    - .sync = synchronize_sched, \
    - .call = call_rcu_sched, \
    -}
    -
    -#define __RCU_BH_SYNC_INIT(name) { \
    - ___RCU_SYNC_INIT(name), \
    - .sync = synchronize_rcu_bh, \
    - .call = call_rcu_bh, \
    -}
    -
    -#define __RCU_SYNC_INIT(name) { \
    - ___RCU_SYNC_INIT(name), \
    - .sync = synchronize_rcu, \
    - .call = call_rcu, \
    -}
    -
    -#define DEFINE_RCU_SCHED_SYNC(name) \
    - struct rcu_sync name = __RCU_SCHED_SYNC_INIT(name)
    -
    -#define DEFINE_RCU_BH_SYNC(name) \
    - struct rcu_sync name = __RCU_BH_SYNC_INIT(name)
    -
    -#define DEFINE_RCU_SYNC(name) \
    - struct rcu_sync name = __RCU_SYNC_INIT(name)
    -
    /**
    * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
    * @rsp: Pointer to rcu_sync structure to use for synchronization
    @@ -85,10 +53,28 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
    return !rsp->gp_state; /* GP_IDLE */
    }

    -enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
    -
    extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
    extern void rcu_sync_enter(struct rcu_sync *);
    extern void rcu_sync_exit(struct rcu_sync *);

    +#define __RCU_SYNC_INITIALIZER(name, type) { \
    + .gp_state = 0, \
    + .gp_count = 0, \
    + .gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
    + .cb_state = 0, \
    + .gp_type = type, \
    + }
    +
    +#define __DEFINE_RCU_SYNC(name, type) \
    + struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
    +
    +#define DEFINE_RCU_SYNC(name) \
    + __DEFINE_RCU_SYNC(name, RCU_SYNC)
    +
    +#define DEFINE_RCU_SCHED_SYNC(name) \
    + __DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
    +
    +#define DEFINE_RCU_BH_SYNC(name) \
    + __DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
    +
    #endif /* _LINUX_RCU_SYNC_H_ */
    diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
    index 0a11df43be23..5a9aa4c394f1 100644
    --- a/kernel/rcu/sync.c
    +++ b/kernel/rcu/sync.c
    @@ -23,6 +23,24 @@
    #include <linux/rcu_sync.h>
    #include <linux/sched.h>

    +static const struct {
    + void (*sync)(void);
    + void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
    +} gp_ops[] = {
    + [RCU_SYNC] = {
    + .sync = synchronize_rcu,
    + .call = call_rcu,
    + },
    + [RCU_SCHED_SYNC] = {
    + .sync = synchronize_sched,
    + .call = call_rcu_sched,
    + },
    + [RCU_BH_SYNC] = {
    + .sync = synchronize_rcu_bh,
    + .call = call_rcu_bh,
    + },
    +};
    +
    enum { GP_IDLE = 0, GP_PENDING, GP_PASSED };
    enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };

    @@ -37,23 +55,7 @@ void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type)
    {
    memset(rsp, 0, sizeof(*rsp));
    init_waitqueue_head(&rsp->gp_wait);
    -
    - switch (type) {
    - case RCU_SYNC:
    - rsp->sync = synchronize_rcu;
    - rsp->call = call_rcu;
    - break;
    -
    - case RCU_SCHED_SYNC:
    - rsp->sync = synchronize_sched;
    - rsp->call = call_rcu_sched;
    - break;
    -
    - case RCU_BH_SYNC:
    - rsp->sync = synchronize_rcu_bh;
    - rsp->call = call_rcu_bh;
    - break;
    - }
    + rsp->gp_type = type;
    }

    /**
    @@ -85,7 +87,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
    BUG_ON(need_wait && need_sync);

    if (need_sync) {
    - rsp->sync();
    + gp_ops[rsp->gp_type].sync();
    rsp->gp_state = GP_PASSED;
    wake_up_all(&rsp->gp_wait);
    } else if (need_wait) {
    @@ -138,7 +140,7 @@ static void rcu_sync_func(struct rcu_head *rcu)
    * to catch a later GP.
    */
    rsp->cb_state = CB_PENDING;
    - rsp->call(&rsp->cb_head, rcu_sync_func);
    + gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
    } else {
    /*
    * We're at least a GP after rcu_sync_exit(); eveybody will now
    @@ -166,7 +168,7 @@ void rcu_sync_exit(struct rcu_sync *rsp)
    if (!--rsp->gp_count) {
    if (rsp->cb_state == CB_IDLE) {
    rsp->cb_state = CB_PENDING;
    - rsp->call(&rsp->cb_head, rcu_sync_func);
    + gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
    } else if (rsp->cb_state == CB_PENDING) {
    rsp->cb_state = CB_REPLAY;
    }
    --
    2.5.2


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