From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3AF7C3F6B0 for ; Thu, 11 Aug 2022 15:51:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236633AbiHKPv3 (ORCPT ); Thu, 11 Aug 2022 11:51:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237006AbiHKPvB (ORCPT ); Thu, 11 Aug 2022 11:51:01 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 081D5979EF; Thu, 11 Aug 2022 08:42:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 98B4C616C2; Thu, 11 Aug 2022 15:42:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 661CBC433D7; Thu, 11 Aug 2022 15:42:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1660232563; bh=xQmukVhejqSSvaIVDFsfMkvhcUx1mL0PI7bqN3mEXus=; h=From:To:Cc:Subject:Date:From; b=d4CXwt1cqNnn59qi82DeBc3VC6j8uMAsfvf/RUV7u+XJFVp2hwcQnaFYQBmdMwGuT ens8eCyDYDXi8U8k87Vada0Xw3uTiSdnzYkRl92HPw0ioYnFpsJ54zgG4LXGVuxb6h l6ICuYjJju0rLx554ZelyWN/htQLON4TlmMxs4IDH3PzoiEvqgUoBxKRIfE1Posy3E s41U0vjlXMf64y9jlAqO3DsCsLBcjQ+nL4hGtLAXCxxpCSCccShBN42anIUXK0zsqo nu6ybCyKpZ6z4M9qXVmqKj/6BQXHltGqB1Ta+2jJpaGybdU431cD4zUwipW+ImqYST InHqQ2dm0O0Zw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Javier Martinez Canillas , Daniel Vetter , Sasha Levin , daniel@ffwll.ch, deller@gmx.de, tzimmermann@suse.de, sam@ravnborg.org, alexander.deucher@amd.com, deng.changcheng@zte.com.cn, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Subject: [PATCH AUTOSEL 5.18 01/93] fbdev: Restart conflicting fb removal loop when unregistering devices Date: Thu, 11 Aug 2022 11:40:55 -0400 Message-Id: <20220811154237.1531313-1-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org From: Javier Martinez Canillas [ Upstream commit 3367aa7d74d240261de2543ddb35531ccad9d884 ] Drivers that want to remove registered conflicting framebuffers prior to register their own framebuffer, call to remove_conflicting_framebuffers(). This function takes the registration_lock mutex, to prevent a race when drivers register framebuffer devices. But if a conflicting framebuffer device is found, the underlaying platform device is unregistered and this will lead to the platform driver .remove callback to be called. Which in turn will call to unregister_framebuffer() that takes the same lock. To prevent this, a struct fb_info.forced_out field was used as indication to unregister_framebuffer() whether the mutex has to be grabbed or not. But this could be unsafe, since the fbdev core is making assumptions about what drivers may or may not do in their .remove callbacks. Allowing to run these callbacks with the registration_lock held can cause deadlocks, since the fbdev core has no control over what drivers do in their removal path. A better solution is to drop the lock before platform_device_unregister(), so unregister_framebuffer() can take it when called from the fbdev driver. The lock is acquired again after the device has been unregistered and at this point the removal loop can be restarted. Since the conflicting framebuffer device has already been removed, the loop would just finish when no more conflicting framebuffers are found. Suggested-by: Daniel Vetter Signed-off-by: Javier Martinez Canillas Reviewed-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20220511113039.1252432-1-javierm@redhat.com Signed-off-by: Sasha Levin --- drivers/video/fbdev/core/fbmem.c | 22 +++++++++++++++------- include/linux/fb.h | 1 - 2 files changed, 15 insertions(+), 8 deletions(-) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 643383d74edc..82880f59ba67 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1566,6 +1566,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, { int i; +restart_removal: /* check all firmware fbs and kick off if the base addr overlaps */ for_each_registered_fb(i) { struct apertures_struct *gen_aper; @@ -1600,12 +1601,23 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a, */ do_unregister_framebuffer(registered_fb[i]); } else if (dev_is_platform(device)) { - registered_fb[i]->forced_out = true; + /* + * Drop the lock because if the device is unregistered, its + * driver will call to unregister_framebuffer(), that takes + * this lock. + */ + mutex_unlock(®istration_lock); platform_device_unregister(to_platform_device(device)); + mutex_lock(®istration_lock); } else { pr_warn("fb%d: cannot remove device\n", i); do_unregister_framebuffer(registered_fb[i]); } + /* + * Restart the removal loop now that the device has been + * unregistered and its associated framebuffer gone. + */ + goto restart_removal; } } } @@ -1946,13 +1958,9 @@ EXPORT_SYMBOL(register_framebuffer); void unregister_framebuffer(struct fb_info *fb_info) { - bool forced_out = fb_info->forced_out; - - if (!forced_out) - mutex_lock(®istration_lock); + mutex_lock(®istration_lock); do_unregister_framebuffer(fb_info); - if (!forced_out) - mutex_unlock(®istration_lock); + mutex_unlock(®istration_lock); } EXPORT_SYMBOL(unregister_framebuffer); diff --git a/include/linux/fb.h b/include/linux/fb.h index 9a77ab615c36..ae399d3ea4f9 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -503,7 +503,6 @@ struct fb_info { } *apertures; bool skip_vt_switch; /* no VT switch on suspend/resume required */ - bool forced_out; /* set when being removed by another driver */ }; static inline struct apertures_struct *alloc_apertures(unsigned int max_num) { -- 2.35.1