From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751743AbcLCWrr (ORCPT ); Sat, 3 Dec 2016 17:47:47 -0500 Received: from mail-db5eur01on0109.outbound.protection.outlook.com ([104.47.2.109]:59680 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751317AbcLCWrp (ORCPT ); Sat, 3 Dec 2016 17:47:45 -0500 X-Greylist: delayed 40096 seconds by postgrey-1.27 at vger.kernel.org; Sat, 03 Dec 2016 17:47:44 EST Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=bhuvanchandra.dv@toradex.com; Subject: Re: [PATCH] tty: serial: fsl_lpuart: fix del_timer_sync() vs timer routine deadlock To: Nikita Yushchenko , Stefan Agner References: <1480674490-24718-1-git-send-email-nikita.yoush@cogentembedded.com> <77e2726b8b84c55f9109ff18dfcfbbdf@agner.ch> CC: Greg Kroah-Hartman , Jiri Slaby , Wei Yongjun , Aaron Brice , Nicolae Rosia , , Chris Healy , From: 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1;AM5PR0501MB2385;7:RX/+Elz6TNYCvL4rdjdtwgHJJCr43G9b0wm5CXEm/PHrRyW6UnLGnf9gX85WySnKDRZVrmkvhQvfl6o7Zcl5YS3mkwdOjsLNdQltNhSjlM86jyvCuMyuRk4pV2uhx9Z2FW/OuWtGP0AtJwdSftR0rMnLdiN9XbdDgcTlAMkj+GrECRrbFVJrP/ueNAaeh9BtPaPSvYAjDnLJ7xdO4RqT6UsXIs5VIKwCviXPnTVoUqfXv4cA1gazaHlgX9+ZFS1XkT2NtIiPnVjR/meUd5jlQWUEOqW6pkR+DTxmPmw+kmCV3eZZ5r+M8Ny7yThk13vxU0Ku3X0gqYAOkq5yF4FkI5RS28aUTvuGci4QrkQKY+h9VwNHxESSEMAt0pqtfQONGAIFmrCaelEYpa7pthzxwinH1K4HCiSW+NX2sMGNcKyg0QtdVHOEU9c4mOZDWmTfiX/U/ukKakdMK8Jwx8uG2A== X-OriginatorOrg: toradex.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Dec 2016 07:06:45.3480 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM5PR0501MB2385 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/03/2016 02:58 AM, Nikita Yushchenko wrote: >>> Problem found via lockdep: >>> >>> - lpuart_set_termios() calls del_timer_sync(&sport->lpuart_timer) while >>> holding sport->port.lock >>> >>> - sport->lpuart_timer routine is lpuart_timer_func() that calls >>> lpuart_copy_rx_to_tty() that acquires same lock. >>> >>> To fix, move Rx DMA stopping out of lock, as it already is in other places >>> in the same file. >>> >>> While at it, also make Rx DMA start/stop code to look the same is in >>> other places in the same file. >> Yeah I saw that too, never really came around to look closer into it. >> >> Thanks for looking into it. >> >> You removed the check whether there was an old configuration, I think >> the idea of that was that we only resize DMA if it was configured >> differently before... > Per my code reading, checking for sport->lpuart_dma_rx_use should be > enough, this flag will be set only if DMA was previously enabled, The check is to make sure the reconfiguration of DMA is done only when the baudrate is altered. -- Bhuvan > >>> + if (sport->lpuart_dma_rx_use) { >>> + if (!lpuart_start_rx_dma(sport)) { >>> sport->lpuart_dma_rx_use = true; >> No need to set to true here, it is guaranteed to be true at this point. > I've seen this... However elsewhere in this file (namely in > lpuart_resume(), in very similar situation, code is exactly the same, > i.e. it sets sport->lpuart_dma_rx_use in both clauses. I thought it > could be for a reason (i.e. for readability). > > Nikita