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UART: FIFO backend: Avoid possible race 

Avoid a possible race when creating the FIFOs, in which one
side may race ahead and start reading from its Rx pipe
before the other side opening its Tx pipe.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>
This commit is contained in:
Alberto Escolar Piedras 2024-02-06 16:30:15 +01:00
parent e783e51aa1
commit 3582b686cc
1 changed files with 21 additions and 14 deletions
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35
src/HW_models/NHW_UART_backend_fifo.c
View File

@ -641,25 +641,32 @@ static void nhw_ufifo_create_fifos(uint inst, struct ufifo_st_t *u_el) {
bs_trace_error_line("Couldn't create UART backend Rx FIFOs\n");
}
u_el->fifo_rx = open(u_el->fifo_Rx_path, O_RDONLY | O_NONBLOCK);
if (u_el->fifo_rx == -1) {
bs_trace_error_line("Couldn't open UART backend Rx FIFOs\n");
/* 1) We first open our read side non-blocking to avoid a deadlock.
* (This open read side, even if provisional, allows the other side to safely start writing to the
* pipe even if it overtakes our step 3) )
*/
int prov_descr = open(u_el->fifo_Rx_path, O_RDONLY | O_NONBLOCK);
if (prov_descr == -1) {
bs_trace_error_line("Couldn't open UART backend Rx FIFO (%i, %s)\n", errno, strerror(errno));
}
/* We clear NONBLOCK so the reads block until data is ready */
int flags = fcntl(u_el->fifo_rx, F_GETFL);
flags ^= O_NONBLOCK;
int ret = fcntl(u_el->fifo_rx, F_SETFL, flags);
if (ret == -1) {
bs_trace_error_line("Unexpected error %i,%s\n",ret, strerror(errno));
}
/* We block here until the other side is connected */
/* 2) We block opening our Tx side until the other side has reached 1) */
u_el->fifo_tx = open(u_el->fifo_Tx_path, O_WRONLY);
if (u_el->fifo_tx == -1) {
bs_trace_error_line("Couldn't open UART backend Tx FIFOs\n");
bs_trace_error_line("Couldn't open UART backend Tx FIFO (%i, %s)\n", errno, strerror(errno));
}
/* 3) And now that we know the other side reached 1), we can block until it reaches 2)
* while creating the descriptor we will actually use */
u_el->fifo_rx = open(u_el->fifo_Rx_path, O_RDONLY);
if (u_el->fifo_rx == -1) {
bs_trace_error_line("Couldn't open UART backend Rx FIFO (%i, %s)\n", errno, strerror(errno));
}
/* At this point we know both pipes are open in both sides.
* We can now close our previous Rx descriptor as we won't use it for anything anymore. */
(void)close(prov_descr);
}
static void nhw_ufifo_backend_cleanup(void) {