dmaengine: pl330: fix double lock

The static bug finder EBA (http://www.iagoabal.eu/eba/) reported the
following double-lock bug:

    Double lock:
    1. spin_lock_irqsave(pch->lock, flags) at pl330_free_chan_resources:2236;
    2. call to function `pl330_release_channel' immediately after;
    3. call to function `dma_pl330_rqcb' in line 1753;
    4. spin_lock_irqsave(pch->lock, flags) at dma_pl330_rqcb:1505.

I have fixed it as suggested by Marek Szyprowski.

First, I have replaced `pch->lock' with `pl330->lock' in functions
`pl330_alloc_chan_resources' and `pl330_free_chan_resources'. This avoids
the double-lock by acquiring a different lock than `dma_pl330_rqcb'.

NOTE that, as a result, `pl330_free_chan_resources' executes
`list_splice_tail_init' on `pch->work_list' under lock `pl330->lock',
whereas in the rest of the code `pch->work_list' is protected by
`pch->lock'. I don't know if this may cause race conditions. Similarly
`pch->cyclic' is written by `pl330_alloc_chan_resources' under
`pl330->lock' but read by `pl330_tx_submit' under `pch->lock'.

Second, I have removed locking from `pl330_request_channel' and
`pl330_release_channel' functions. Function `pl330_request_channel' is
only called from `pl330_alloc_chan_resources', so the lock is already
held. Function `pl330_release_channel' is called from
`pl330_free_chan_resources', which already holds the lock, and from
`pl330_del'. Function `pl330_del' is called in an error path of
`pl330_probe' and at the end of `pl330_remove', but I assume that there
cannot be concurrent accesses to the protected data at those points.

Signed-off-by: Iago Abal <mail@iagoabal.eu>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

path: root/sound/core/seq/seq_lock.h

#ifndef __SND_SEQ_LOCK_H
#define __SND_SEQ_LOCK_H

#include <linux/sched.h>

#if defined(CONFIG_SMP) || defined(CONFIG_SND_DEBUG)

typedef atomic_t snd_use_lock_t;

/* initialize lock */
#define snd_use_lock_init(lockp) atomic_set(lockp, 0)

/* increment lock */
#define snd_use_lock_use(lockp) atomic_inc(lockp)

/* release lock */
#define snd_use_lock_free(lockp) atomic_dec(lockp)

/* wait until all locks are released */
void snd_use_lock_sync_helper(snd_use_lock_t *lock, const char *file, int line);
#define snd_use_lock_sync(lockp) snd_use_lock_sync_helper(lockp, __BASE_FILE__, __LINE__)

#else /* SMP || CONFIG_SND_DEBUG */

typedef spinlock_t snd_use_lock_t;	/* dummy */
#define snd_use_lock_init(lockp) /**/
#define snd_use_lock_use(lockp) /**/
#define snd_use_lock_free(lockp) /**/
#define snd_use_lock_sync(lockp) /**/

#endif /* SMP || CONFIG_SND_DEBUG */

#endif /* __SND_SEQ_LOCK_H */