Messages in this thread |  | | From | Anand Moon <> | Date | Sun, 21 Feb 2016 08:29:36 +0530 | Subject | Re: [PATCHv2] serial: samsung: drop the spinlock around uart_write_wakeup |
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Hi Krzysztof,
On 21 February 2016 at 07:07, Krzysztof Kozlowski <k.kozlowski@samsung.com> wrote: > 2016-02-20 4:30 GMT+09:00 Peter Hurley <peter@hurleysoftware.com>: >> [ +cc Krzysztof Kozlowski ] >> >> On 02/18/2016 09:15 PM, Anand Moon wrote: >>> From: Anand Moon <linux.amoon@gmail.com> >>> >>> drop the spin_unlock/lock around uart_write_wakeup to protect >>> write wakeup for uart port. >> >> What Krzysztof was saying wrt v1 of this patch is that the >> changelog should provide as much information as possible to >> the maintainer(s) and driver author(s), and that you should >> test that outcome. >> >> Here's what I would have written for a commit message: >> >> >> Remove deadlock workaround for line disciplines that invoke >> the tty driver's write() method directly from their write_wakeup() >> method. As documented for the write_wakeup() line discipline method >> in tty_ldisc.h, line disciplines must not attempt i/o directly >> from write_wakeup() as this will deadlock. Reviews of in-tree line >> disciplines confirm all defer i/o. >> >> NB: This workaround was added in commit c15c3747ee32 >> ("serial: samsung: fix potential soft lockup during uart write") >> which notes both slip and bluetooth hci attempt i/o directly from >> write_wakeup(). These issues were fixed in commits 661f7fda21b1 >> ("slip: Fix deadlock in write_wakeup") and da64c27d3c93 >> ("bluetooth: hci_ldisc: fix deadlock condition"), respectively. > > Thanks Peter for thorough analysis. It shouldn't be done by you but by > the patch submitter... and I have big worries that Anand did not > perform that analysis. > > Anand, could you at least test that this lockup does not happen > anymore? You will need board with Bluetooth for that (and not USB > Bluetooth...). If you cannot test it, maybe guys from Polish R&D could > help you (Cc-ed), because they were working on DMA for serial used in > Bluetooth. > > Best regards, > Krzysztof
I have looked into the history of the changes, commit c15c3747ee32 (serial: samsung: fix potential soft lockup during uart write) was added long time ago, that's why have missed this.
I don't have on-board Bluetooth enable boards with me, so if their is potential lockup you people observer do not consider this patch.
My change's were on the perception of the locking/unlocking.
Thanks for your inputs.
Best regards, -Anand Moon
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