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/tools/build/feature/test-libunwind.c

#include <libunwind.h>
#include <stdlib.h>

extern int UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
                                      unw_word_t ip,
                                      unw_dyn_info_t *di,
                                      unw_proc_info_t *pi,
                                      int need_unwind_info, void *arg);


#define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)

static unw_accessors_t accessors;

int main(void)
{
	unw_addr_space_t addr_space;

	addr_space = unw_create_addr_space(&accessors, 0);
	if (addr_space)
		return 0;

	unw_init_remote(NULL, addr_space, NULL);
	dwarf_search_unwind_table(addr_space, 0, NULL, NULL, 0, NULL);

	return 0;
}