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9407f5c3ec
Currently, srcu_read_lock_lite() uses the SRCU_READ_FLAVOR_LITE bit in ->srcu_reader_flavor to communicate to the grace-period processing in srcu_readers_active_idx_check() that the smp_mb() must be replaced by a synchronize_rcu(). Unfortunately, ->srcu_reader_flavor is not updated unless the kernel is built with CONFIG_PROVE_RCU=y. Therefore in all kernels built with CONFIG_PROVE_RCU=n, srcu_readers_active_idx_check() incorrectly uses smp_mb() instead of synchronize_rcu() for srcu_struct structures whose readers use srcu_read_lock_lite(). This commit therefore causes Tree SRCU srcu_read_lock_lite() to unconditionally update ->srcu_reader_flavor so that srcu_readers_active_idx_check() can make the correct choice. Reported-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com> Closes: https://lore.kernel.org/all/d07e8f4a-d5ff-4c8e-8e61-50db285c57e9@amd.com/ Fixes: c0f08d6b5a61 ("srcu: Add srcu_read_lock_lite() and srcu_read_unlock_lite()") Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
103 lines
3.2 KiB
C
103 lines
3.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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* Sleepable Read-Copy Update mechanism for mutual exclusion,
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* tiny variant.
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*
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* Copyright (C) IBM Corporation, 2017
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*
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* Author: Paul McKenney <paulmck@linux.ibm.com>
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*/
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#ifndef _LINUX_SRCU_TINY_H
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#define _LINUX_SRCU_TINY_H
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#include <linux/swait.h>
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struct srcu_struct {
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short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
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u8 srcu_gp_running; /* GP workqueue running? */
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u8 srcu_gp_waiting; /* GP waiting for readers? */
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unsigned long srcu_idx; /* Current reader array element in bit 0x2. */
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unsigned long srcu_idx_max; /* Furthest future srcu_idx request. */
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struct swait_queue_head srcu_wq;
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/* Last srcu_read_unlock() wakes GP. */
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struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
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struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
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struct work_struct srcu_work; /* For driving grace periods. */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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struct lockdep_map dep_map;
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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};
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void srcu_drive_gp(struct work_struct *wp);
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#define __SRCU_STRUCT_INIT(name, __ignored, ___ignored) \
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{ \
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.srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
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.srcu_cb_tail = &name.srcu_cb_head, \
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.srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
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__SRCU_DEP_MAP_INIT(name) \
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}
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/*
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* This odd _STATIC_ arrangement is needed for API compatibility with
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* Tree SRCU, which needs some per-CPU data.
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*/
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#define DEFINE_SRCU(name) \
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struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
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#define DEFINE_STATIC_SRCU(name) \
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static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
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// Dummy structure for srcu_notifier_head.
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struct srcu_usage { };
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#define __SRCU_USAGE_INIT(name) { }
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void synchronize_srcu(struct srcu_struct *ssp);
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/*
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* Counts the new reader in the appropriate per-CPU element of the
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* srcu_struct. Can be invoked from irq/bh handlers, but the matching
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* __srcu_read_unlock() must be in the same handler instance. Returns an
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* index that must be passed to the matching srcu_read_unlock().
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*/
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static inline int __srcu_read_lock(struct srcu_struct *ssp)
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{
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int idx;
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preempt_disable(); // Needed for PREEMPT_AUTO
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idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
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WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
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preempt_enable();
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return idx;
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}
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static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
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{
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synchronize_srcu(ssp);
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}
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static inline void srcu_barrier(struct srcu_struct *ssp)
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{
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synchronize_srcu(ssp);
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}
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#define srcu_check_read_flavor(ssp, read_flavor) do { } while (0)
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#define srcu_check_read_flavor_lite(ssp) do { } while (0)
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/* Defined here to avoid size increase for non-torture kernels. */
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static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
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char *tt, char *tf)
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{
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int idx;
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idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
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pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n",
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tt, tf, idx,
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data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
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data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])),
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data_race(READ_ONCE(ssp->srcu_idx)),
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data_race(READ_ONCE(ssp->srcu_idx_max)));
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}
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#endif
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