cregit-Linux how code gets into the kernel

Release 4.15 kernel/locking/percpu-rwsem.c

Directory: kernel/locking
#include <linux/atomic.h>
#include <linux/rwsem.h>
#include <linux/percpu.h>
#include <linux/lockdep.h>
#include <linux/percpu-rwsem.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/errno.h>

int __percpu_init_rwsem(struct percpu_rw_semaphore *sem, const char *name, struct lock_class_key *rwsem_key) { sem->read_count = alloc_percpu(int); if (unlikely(!sem->read_count)) return -ENOMEM; /* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */ rcu_sync_init(&sem->rss, RCU_SCHED_SYNC); __init_rwsem(&sem->rw_sem, name, rwsem_key); rcuwait_init(&sem->writer); sem->readers_block = 0; return 0; }


Oleg Nesterov6274.70%466.67%
Peter Zijlstra2024.10%116.67%
Davidlohr Bueso A11.20%116.67%

void percpu_free_rwsem(struct percpu_rw_semaphore *sem) { /* * XXX: temporary kludge. The error path in alloc_super() * assumes that percpu_free_rwsem() is safe after kzalloc(). */ if (!sem->read_count) return; rcu_sync_dtor(&sem->rss); free_percpu(sem->read_count); sem->read_count = NULL; /* catch use after free bugs */ }


Oleg Nesterov3380.49%375.00%
Peter Zijlstra819.51%125.00%

int __percpu_down_read(struct percpu_rw_semaphore *sem, int try) { /* * Due to having preemption disabled the decrement happens on * the same CPU as the increment, avoiding the * increment-on-one-CPU-and-decrement-on-another problem. * * If the reader misses the writer's assignment of readers_block, then * the writer is guaranteed to see the reader's increment. * * Conversely, any readers that increment their sem->read_count after * the writer looks are guaranteed to see the readers_block value, * which in turn means that they are guaranteed to immediately * decrement their sem->read_count, so that it doesn't matter that the * writer missed them. */ smp_mb(); /* A matches D */ /* * If !readers_block the critical section starts here, matched by the * release in percpu_up_write(). */ if (likely(!smp_load_acquire(&sem->readers_block))) return 1; /* * Per the above comment; we still have preemption disabled and * will thus decrement on the same CPU as we incremented. */ __percpu_up_read(sem); if (try) return 0; /* * We either call schedule() in the wait, or we'll fall through * and reschedule on the preempt_enable() in percpu_down_read(). */ preempt_enable_no_resched(); /* * Avoid lockdep for the down/up_read() we already have them. */ __down_read(&sem->rw_sem); this_cpu_inc(*sem->read_count); __up_read(&sem->rw_sem); preempt_disable(); return 1; }


Oleg Nesterov4452.38%480.00%
Peter Zijlstra4047.62%120.00%

void __percpu_up_read(struct percpu_rw_semaphore *sem) { smp_mb(); /* B matches C */ /* * In other words, if they see our decrement (presumably to aggregate * zero, as that is the only time it matters) they will also see our * critical section. */ __this_cpu_dec(*sem->read_count); /* Prod writer to recheck readers_active */ rcuwait_wake_up(&sem->writer); }


Oleg Nesterov1753.12%250.00%
Peter Zijlstra1443.75%125.00%
Davidlohr Bueso A13.12%125.00%

EXPORT_SYMBOL_GPL(__percpu_up_read); #define per_cpu_sum(var) \ ({ \ typeof(var) __sum = 0; \ int cpu; \ compiletime_assert_atomic_type(__sum); \ for_each_possible_cpu(cpu) \ __sum += per_cpu(var, cpu); \ __sum; \ }) /* * Return true if the modular sum of the sem->read_count per-CPU variable is * zero. If this sum is zero, then it is stable due to the fact that if any * newly arriving readers increment a given counter, they will immediately * decrement that same counter. */
static bool readers_active_check(struct percpu_rw_semaphore *sem) { if (per_cpu_sum(*sem->read_count) != 0) return false; /* * If we observed the decrement; ensure we see the entire critical * section. */ smp_mb(); /* C matches B */ return true; }


Peter Zijlstra1852.94%150.00%
Oleg Nesterov1647.06%150.00%

void percpu_down_write(struct percpu_rw_semaphore *sem) { /* Notify readers to take the slow path. */ rcu_sync_enter(&sem->rss); down_write(&sem->rw_sem); /* * Notify new readers to block; up until now, and thus throughout the * longish rcu_sync_enter() above, new readers could still come in. */ WRITE_ONCE(sem->readers_block, 1); smp_mb(); /* D matches A */ /* * If they don't see our writer of readers_block, then we are * guaranteed to see their sem->read_count increment, and therefore * will wait for them. */ /* Wait for all now active readers to complete. */ rcuwait_wait_event(&sem->writer, readers_active_check(sem)); }


Oleg Nesterov3460.71%360.00%
Peter Zijlstra2035.71%120.00%
Davidlohr Bueso A23.57%120.00%

void percpu_up_write(struct percpu_rw_semaphore *sem) { /* * Signal the writer is done, no fast path yet. * * One reason that we cannot just immediately flip to readers_fast is * that new readers might fail to see the results of this writer's * critical section. * * Therefore we force it through the slow path which guarantees an * acquire and thereby guarantees the critical section's consistency. */ smp_store_release(&sem->readers_block, 0); /* * Release the write lock, this will allow readers back in the game. */ up_write(&sem->rw_sem); /* * Once this completes (at least one RCU-sched grace period hence) the * reader fast path will be available again. Safe to use outside the * exclusive write lock because its counting. */ rcu_sync_exit(&sem->rss); }


Oleg Nesterov2358.97%266.67%
Peter Zijlstra1641.03%133.33%


Overall Contributors

Oleg Nesterov25358.56%660.00%
Peter Zijlstra14734.03%110.00%
Paul E. McKenney235.32%110.00%
Daeho Jeong51.16%110.00%
Davidlohr Bueso A40.93%110.00%
Directory: kernel/locking
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.
Created with cregit.