[PATCH] mlx: Fix a possible sleep-under-mutex bug in mlx_alloccmd

[Jia-Ju Bai]

The driver may sleep under a mutex, and the function call path is:
mlx_attach [line 432: acquire the mutex]
  mlx_enquire
    mlx_alloccmd
      bus_dmamap_create(BUS_DMA_WAITOK) --> may sleep

The possible fix of this bug is to replace "BUS_DMA_WAITOK" in bus_dmamap_create with "BUS_DMA_NOWAIT".

This bug is found by a static analysis tool written by myself, and it is
checked by my review of the FreeBSD code.

Signed-off-by: Jia-Ju Bai <baijiaju1990 at 163.com>
---
 sys/dev/mlx/mlx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sys/dev/mlx/mlx.c b/sys/dev/mlx/mlx.c
index e3b09582a36..c2e8ba3c595 100644
--- a/sys/dev/mlx/mlx.c
+++ b/sys/dev/mlx/mlx.c
@@ -2426,7 +2426,8 @@ mlx_alloccmd(struct mlx_softc *sc)
 	mc = (struct mlx_command *)malloc(sizeof(*mc), M_DEVBUF, M_NOWAIT | M_ZERO);
 	if (mc != NULL) {
 	    mc->mc_sc = sc;
-	    error = bus_dmamap_create(sc->mlx_buffer_dmat, 0, &mc->mc_dmamap);
+	    error = bus_dmamap_create(sc->mlx_buffer_dmat, BUS_DMA_NOWAIT, 
+							&mc->mc_dmamap);
 	    if (error) {
 		free(mc, M_DEVBUF);
 		return(NULL);
-- 
2.13.0