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sched/sem_rw: convert read-lock to write-lock when self already holds a write-lock

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If the write lock is already held by oneself and sine the write
lock can be recursively held, so, this operation can be converted to a write
lock to avoid deadlock.

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>
This commit is contained in:
dongjiuzhu1 2024-10-02 23:29:22 +08:00 • committed by GUIDINGLI
parent 1c2856dfcb
commit 2e3a6acaa2
1 changed files with 40 additions and 0 deletions
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40
sched/semaphore/sem_rw.c
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@ -68,6 +68,17 @@ int down_read_trylock(FAR rw_semaphore_t *rwsem)
{
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
/* if the write lock is already held by oneself and since the write lock
* can be recursively held, so, this operation can be converted to a write
* lock to avoid deadlock.
*/
if (rwsem->holder == _SCHED_GETTID())
{
rwsem->writer++;
goto out;
}
if (rwsem->writer > 0)
{
spin_unlock_irqrestore(&rwsem->protected, flags);
@ -80,6 +91,7 @@ int down_read_trylock(FAR rw_semaphore_t *rwsem)
rwsem->reader++;
out:
spin_unlock_irqrestore(&rwsem->protected, flags);
return 1;
@ -104,6 +116,17 @@ void down_read(FAR rw_semaphore_t *rwsem)
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
/* if the write lock is already held by oneself and since the write lock
* can be recursively held, so, this operation can be converted to a write
* lock to avoid deadlock.
*/
if (rwsem->holder == _SCHED_GETTID())
{
rwsem->writer++;
goto out;
}
while (rwsem->writer > 0)
{
rwsem->waiter++;
@ -119,6 +142,7 @@ void down_read(FAR rw_semaphore_t *rwsem)
rwsem->reader++;
out:
spin_unlock_irqrestore(&rwsem->protected, flags);
}
@ -137,6 +161,21 @@ void up_read(FAR rw_semaphore_t *rwsem)
{
irqstate_t flags = spin_lock_irqsave(&rwsem->protected);
/* when releasing a read lock and holder is oneself, the read lock is a
* write lock that has been converted, so it should be released according
* to the procedures for releasing a write lock.
*/
if (rwsem->holder == _SCHED_GETTID())
{
if (--rwsem->writer <= 0)
{
rwsem->holder = RWSEM_NO_HOLDER;
}
goto out;
}
DEBUGASSERT(rwsem->reader > 0);
rwsem->reader--;
@ -146,6 +185,7 @@ void up_read(FAR rw_semaphore_t *rwsem)
up_wait(rwsem);
}
out:
spin_unlock_irqrestore(&rwsem->protected, flags);
}