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locking/percpu-rwsem: add freezable alternative to down_read

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Percpu-rwsems are used for superblock locking.  However, we know the
read percpu-rwsem we take for sb_start_write() on a frozen filesystem
needs not to inhibit system from suspending or hibernating.  That
means it needs to wait with TASK_UNINTERRUPTIBLE | TASK_FREEZABLE.

Introduce a new percpu_down_read_freezable() that allows us to control
whether TASK_FREEZABLE is added to the wait flags.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Link: https://lore.kernel.org/r/20250327140613.25178-2-James.Bottomley@HansenPartnership.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
James Bottomley 2025-03-27 10:06:10 -04:00 committed by Christian Brauner
parent 0af2f6be1b
commit 559b3bbfa9
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GPG Key ID: 91C61BC06578DCA2
2 changed files with 24 additions and 9 deletions
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20
include/linux/percpu-rwsem.h
View File

@ -43,9 +43,10 @@ is_static struct percpu_rw_semaphore name = { \
#define DEFINE_STATIC_PERCPU_RWSEM(name) \
__DEFINE_PERCPU_RWSEM(name, static)
extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool, bool);
static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
static inline void percpu_down_read_internal(struct percpu_rw_semaphore *sem,
bool freezable)
{
might_sleep();
@ -63,7 +64,7 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
if (likely(rcu_sync_is_idle(&sem->rss)))
this_cpu_inc(*sem->read_count);
else
__percpu_down_read(sem, false); /* Unconditional memory barrier */
__percpu_down_read(sem, false, freezable); /* Unconditional memory barrier */
/*
* The preempt_enable() prevents the compiler from
* bleeding the critical section out.
@ -71,6 +72,17 @@ static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
preempt_enable();
}
static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
{
percpu_down_read_internal(sem, false);
}
static inline void percpu_down_read_freezable(struct percpu_rw_semaphore *sem,
bool freeze)
{
percpu_down_read_internal(sem, freeze);
}
static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
bool ret = true;
@ -82,7 +94,7 @@ static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
if (likely(rcu_sync_is_idle(&sem->rss)))
this_cpu_inc(*sem->read_count);
else
ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
ret = __percpu_down_read(sem, true, false); /* Unconditional memory barrier */
preempt_enable();
/*
* The barrier() from preempt_enable() prevents the compiler from

13
kernel/locking/percpu-rwsem.c
View File

@ -138,7 +138,8 @@ static int percpu_rwsem_wake_function(struct wait_queue_entry *wq_entry,
return !reader; /* wake (readers until) 1 writer */
}
static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader,
bool freeze)
{
DEFINE_WAIT_FUNC(wq_entry, percpu_rwsem_wake_function);
bool wait;
@ -156,7 +157,8 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
spin_unlock_irq(&sem->waiters.lock);
while (wait) {
set_current_state(TASK_UNINTERRUPTIBLE);
set_current_state(TASK_UNINTERRUPTIBLE |
(freeze ? TASK_FREEZABLE : 0));
if (!smp_load_acquire(&wq_entry.private))
break;
schedule();
@ -164,7 +166,8 @@ static void percpu_rwsem_wait(struct percpu_rw_semaphore *sem, bool reader)
__set_current_state(TASK_RUNNING);
}
bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try,
bool freeze)
{
if (__percpu_down_read_trylock(sem))
return true;
@ -174,7 +177,7 @@ bool __sched __percpu_down_read(struct percpu_rw_semaphore *sem, bool try)
trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_READ);
preempt_enable();
percpu_rwsem_wait(sem, /* .reader = */ true);
percpu_rwsem_wait(sem, /* .reader = */ true, freeze);
preempt_disable();
trace_contention_end(sem, 0);
@ -237,7 +240,7 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem)
*/
if (!__percpu_down_write_trylock(sem)) {
trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE);
percpu_rwsem_wait(sem, /* .reader = */ false);
percpu_rwsem_wait(sem, /* .reader = */ false, false);
contended = true;
}