spi: Fix memory leak on splited transfers

In the prepare_message callback the bus driver has the
opportunity to split a transfer into smaller chunks.
spi_map_msg is done after prepare_message.

Function spi_res_release releases the splited transfers
in the message. Therefore spi_res_release should be called
after spi_map_msg.

The previous try at this was commit c9ba7a16d0f1
which released the splited transfers after
spi_finalize_current_message had been called.
This introduced a race since the message struct could be
out of scope because the spi_sync call got completed.

Fixes this leak on spi bus driver spi-bcm2835.c when transfer
size is greater than 65532:

Kmemleak:
sg_alloc_table+0x28/0xc8
spi_map_buf+0xa4/0x300
__spi_pump_messages+0x370/0x748
__spi_sync+0x1d4/0x270
spi_sync+0x34/0x58
spi_test_execute_msg+0x60/0x340 [spi_loopback_test]
spi_test_run_iter+0x548/0x578 [spi_loopback_test]
spi_test_run_test+0x94/0x140 [spi_loopback_test]
spi_test_run_tests+0x150/0x180 [spi_loopback_test]
spi_loopback_test_probe+0x50/0xd0 [spi_loopback_test]
spi_drv_probe+0x84/0xe0

Signed-off-by: Gustav Wiklander <gustavwi@axis.com>
Link: https://lore.kernel.org/r/20200908151129.15915-1-gustav.wiklander@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 92b8fb4..832926b 100644 (file)
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1327,8 +1327,6 @@ out:
        if (msg->status && ctlr->handle_err)
                ctlr->handle_err(ctlr, msg);
 
-       spi_res_release(ctlr, msg);
-
        spi_finalize_current_message(ctlr);
 
        return ret;
@@ -1727,6 +1725,13 @@ void spi_finalize_current_message(struct spi_controller *ctlr)
 
        spi_unmap_msg(ctlr, mesg);
 
+       /* In the prepare_messages callback the spi bus has the opportunity to
+        * split a transfer to smaller chunks.
+        * Release splited transfers here since spi_map_msg is done on the
+        * splited transfers.
+        */
+       spi_res_release(ctlr, mesg);
+
        if (ctlr->cur_msg_prepared && ctlr->unprepare_message) {
                ret = ctlr->unprepare_message(ctlr, mesg);
                if (ret) {