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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
2 changed files with 24 additions and 9 deletions
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13
kernel/locking/percpu-rwsem.c
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@@ -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;
}