On Thu, 2025-03-27 at 15:24 +0000, Yannick Serafini wrote: > I've recently encountered race conditions related to SIM hot-swapping > events and wanted to delve deeper into this mechanism. > > The race conditions occurred in scenarios where I failed to insert > the SIM card correctly on the first attempt. > Here's the problematic sequence: > 0. URC for hot swap has been enabled in previous session (Fibocom > MC610 modem memorizes this parameter in NVM) > 1. Partial SIM insertion triggers "+SIM: Inserted" URC > 2. ModemManager begins modem creation process > 3. Before completion, a "+SIM: Removed" URC is received (due to > unstable insertion) > 4. SIM is finally inserted correctly > 5. ModemManager completes modem setup with SIM apparently detected > > The issue is that the unsolicited message "+SIM: Removed" arrives > before the hot-swap handler is registered, causing this URC data to > end up in unrelated modem properties (like manufacturer information). > Sometimes, the SIM state incorrectly shows "sim-failure" and I > suspect it is related.
I would agree. > > To address this, I implemented a default unsolicited message handler > in setup_port (same as in the Cinterion implementation) to catch URCs > that arrive before the hot-swap handler is registered. I think that's the right thing to do. > > This works initially, but fails when the SIM is activated because of > the following sequence: > 1. Modem is detected > 2. port_setup() is called > 3. hot swap setting is configured > 4. SIM is unlocked > 5. Modem is recreated Note that this step should no longer be the case after https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/1318 Does having that MR in the code you're running change behavior or the sequence here? I suspect it helps, but may just be papering over the underlying logic issues. > 6. port_setup() is called again > 7. setup_sim_hot_swap() is NOT called because it's inhibited by the > sim_hot_swap_configured flag in mm-iface-modem.c Hmm. If the modem is in fact getting re-created, that should be a completely new Modem object and MMIfaceModem though. Thus it should go back to sim_hot_swap_configured=FALSE? But I don't doubt that SIM events could go missing due to when the URCs get enabled/disabled and parsed. Thanks, Dan > > At this point, only the general handler defined in port_setup() > remains active, which overrides the specialized handler from the > initial hot swap configuration. > This causes SIM events to be ignored. > > I don't really understand why cleanup_sim_hot_swap is not supposed to > disable the hot swap feature by sending the AT command to disable the > URC from the modem and obviously clear the sim_hot_swap_configured > flag, ideally with a cleanup_sim_hot_swap_finish. > That would however not handle the case of a crash letting hot swap > enabled in the modem so an approach to handle URC from the beginning > (or least as soon as possible) would be probably ideal. > > I'm interested in your opinion here, I think my issue is mainly > related to the fact the hot swap feature is persistent in the modem > but more generally, do you see a good approach to fix this issue?
