shell bypass sample not outputting to serial

[roni1234321]

Describe the bug

when running the shell bypass sample the shell gets stuck and to text is not printed to terminal, and shell is locked.
after short inspection it seems that shell_fprintf() fails to take the internal shell mutex (sh->ctx->lock_sem) and printing is dropped.

possible fix is to unlock shell before and re-lock after calling bypass cb. snippet from shell.c:

		if (bypass) {
#if defined(CONFIG_SHELL_BACKEND_RTT) && defined(CONFIG_SEGGER_RTT_BUFFER_SIZE_DOWN)
			uint8_t buf[CONFIG_SEGGER_RTT_BUFFER_SIZE_DOWN];
#else
			uint8_t buf[16];
#endif

			(void)sh->iface->api->read(sh->iface, buf,
							sizeof(buf), &count);
			if (count) {
				z_flag_cmd_ctx_set(sh, true);
				z_shell_unlock(sh); // add this 
				bypass(sh, buf, count);
				z_shell_lock(sh); //and this
				z_flag_cmd_ctx_set(sh, false);
				/* Check if bypass mode ended. */
				if (!(volatile shell_bypass_cb_t *)sh->ctx->bypass) {
					state_set(sh, SHELL_STATE_ACTIVE);
				} else {
					continue;
				}
			}

			return;
		}

this fix was tested and seems to fix the issue.

Regression

• This is a regression.

Steps to reproduce

1. build shell_module sample
2. flash and run on nucleo_l476rg
3. type 'bypass' cmd in shell.
4. shell will freeze

Relevant log output

uart:~$ bypass
Bypass started, press ctrl-x ctrl-q to escape
0a |

at this point shell freezes

Impact

Showstopper – Prevents release or major functionality; system unusable.

Environment

Windows 11
zephyr 4.2.0

Additional Context

this regression started after updating zephyr from v4.0.0 to 4.2.0

[henrikbrixandersen]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.yml Do not leave fields empty.

[roni1234321]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.yml Do not leave fields empty.

sorry about that, fixed it.

[jakub-uC]

@roni1234321 Thank you very much for this fix!
In general, this example slightly stretches the shell API. Specifically, it uses the shell_print function while being in the shell context — which, as clearly stated in the API, can lead to a deadlock. :(

It’s strange that this issue only surfaced now. Once again, thank you for spotting it.
Your solution is perfectly valid, though it’s a bit of a hack, which makes future maintenance a bit harder. I’ll merge your proposal and add an appropriate comment in the code.