Messages in this thread | | | Date | Thu, 15 Jul 2021 09:57:22 -0700 | From | Bhaumik Bhatt <> | Subject | Re: [BUG] bus: mhi: possible ABBA deadlock in mhi_pm_m0_transition() and mhi_send_cmd() |
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On 2021-07-15 02:45 AM, Jia-Ju Bai wrote: > Hello, > > I find there is a possible ABBA deadlock in the MHI driver in Linux > 5.10: > > In mhi_pm_m0_transition(): > 262: read_lock_bh(&mhi_cntrl->pm_lock); > 281: spin_lock_irq(&mhi_cmd->lock); > > In mhi_send_cmd(): > 1181: spin_lock_bh(&mhi_cmd->lock); > 1207: read_lock_bh(&mhi_cntrl->pm_lock); > > When mhi_pm_m0_transition() and mhi_send_cmd() are concurrently > executed, the deadlock can occur. > > I check the code and find a possible case of such concurrent execution: > > #CPU1: > mhi_poll (mhi_event->process_event(...)) > mhi_process_ctrl_ev_ring > mhi_pm_m0_transition > > #CPU2: > mhi_prepare_for_transfer > mhi_prepare_channel > mhi_send_cmd > > Note that mhi_poll() and mhi_prepare_for_transfer() are both exported > by EXPORT_SYMBOL. > Thus, I guess these two functions could be concurrently called by a MHI > driver. > > I am not quite sure whether this possible deadlock is real and how to > fix it if it is real. > Any feedback would be appreciated, thanks :) > > > Best wishes, > Jia-Ju Bai
Few pointers from your example:
1. mhi_poll() is currently not used by any client upstream yet. 2. Polling is not to be used for single event ring (shared control + data) cases since it is meant to be for client drivers with dedicated data packets only. 3. mhi_send_cmd() will always be called after an mhi_pm_m0_transition() has completed by design since we wait for the device to be held in M0 prior to it.
Would like to know what Mani and Hemant have to say. I don't think we can run in to the scenario from your example so we should be safe.
Thanks, Bhaumik --- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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