From: Javier Martinez Canillas <javierm@redhat.com> To: Daniel Vetter <daniel.vetter@ffwll.ch>, DRI Development <dri-devel@lists.freedesktop.org> Cc: Du Cheng <ducheng2@gmail.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Intel Graphics Development <intel-gfx@lists.freedesktop.org>, Zheyu Ma <zheyuma97@gmail.com>, Matthew Wilcox <willy@infradead.org>, Nathan Chancellor <nathan@kernel.org>, Claudio Suarez <cssk@net-c.es>, Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter <daniel.vetter@intel.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Sam Ravnborg <sam@ravnborg.org>, Helge Deller <deller@gmx.de>, Guenter Roeck <linux@roeck-us.net> Subject: Re: [PATCH] fbcon: Fix delayed takeover locking Date: Wed, 13 Apr 2022 11:16:08 +0200 [thread overview] Message-ID: <955400a5-a785-57af-92d4-42710c55ce99@redhat.com> (raw) In-Reply-To: <20220413082128.348186-1-daniel.vetter@ffwll.ch> Hello Daniel, On 4/13/22 10:21, Daniel Vetter wrote: > I messed up the delayed takover path in the locking conversion in > 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister"). > Maybe a few more words of what the issue is ? Something like the following: If CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER is enabled, fbcon take-over doesn't take place when calling fbcon_fb_registered(). Instead, is deferred using a workqueue and its fbcon_register_existing_fbs() function calls to fbcon_fb_registered() again for each registered fbcon fb. This leads to the console_lock tried to be held twice, causing a deadlock. > Fix it by re-extracting the lockless function and using it in the > delayed takeover path, where we need to hold the lock already to > iterate over the list of already registered fb. Well the current code > still is broken in there (since the list is protected by a > registration_lock, which we can't take here because it nests the other > way round with console_lock), but in the future this will be a list > protected by console_lock when this is all sorted out. > [snip] > > -/* called with console_lock held */ > void fbcon_fb_unbind(struct fb_info *info) > { > int i, new_idx = -1; > @@ -2822,7 +2821,6 @@ void fbcon_fb_unbind(struct fb_info *info) > console_unlock(); > } > > -/* called with console_lock held */ > void fbcon_fb_unregistered(struct fb_info *info) > { Removing these comments feels like should be in a separate patch or at least mention in the patch description that should had been removed in the commit 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister"), that made these functions to be called without the console_lock being held. The changes themselves look good to me. Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat
WARNING: multiple messages have this Message-ID (diff)
From: Javier Martinez Canillas <javierm@redhat.com> To: Daniel Vetter <daniel.vetter@ffwll.ch>, DRI Development <dri-devel@lists.freedesktop.org> Cc: Du Cheng <ducheng2@gmail.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Intel Graphics Development <intel-gfx@lists.freedesktop.org>, Zheyu Ma <zheyuma97@gmail.com>, Matthew Wilcox <willy@infradead.org>, Nathan Chancellor <nathan@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>, Daniel Vetter <daniel.vetter@intel.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Sam Ravnborg <sam@ravnborg.org>, Helge Deller <deller@gmx.de>, Guenter Roeck <linux@roeck-us.net> Subject: Re: [Intel-gfx] [PATCH] fbcon: Fix delayed takeover locking Date: Wed, 13 Apr 2022 11:16:08 +0200 [thread overview] Message-ID: <955400a5-a785-57af-92d4-42710c55ce99@redhat.com> (raw) In-Reply-To: <20220413082128.348186-1-daniel.vetter@ffwll.ch> Hello Daniel, On 4/13/22 10:21, Daniel Vetter wrote: > I messed up the delayed takover path in the locking conversion in > 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister"). > Maybe a few more words of what the issue is ? Something like the following: If CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER is enabled, fbcon take-over doesn't take place when calling fbcon_fb_registered(). Instead, is deferred using a workqueue and its fbcon_register_existing_fbs() function calls to fbcon_fb_registered() again for each registered fbcon fb. This leads to the console_lock tried to be held twice, causing a deadlock. > Fix it by re-extracting the lockless function and using it in the > delayed takeover path, where we need to hold the lock already to > iterate over the list of already registered fb. Well the current code > still is broken in there (since the list is protected by a > registration_lock, which we can't take here because it nests the other > way round with console_lock), but in the future this will be a list > protected by console_lock when this is all sorted out. > [snip] > > -/* called with console_lock held */ > void fbcon_fb_unbind(struct fb_info *info) > { > int i, new_idx = -1; > @@ -2822,7 +2821,6 @@ void fbcon_fb_unbind(struct fb_info *info) > console_unlock(); > } > > -/* called with console_lock held */ > void fbcon_fb_unregistered(struct fb_info *info) > { Removing these comments feels like should be in a separate patch or at least mention in the patch description that should had been removed in the commit 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister"), that made these functions to be called without the console_lock being held. The changes themselves look good to me. Reviewed-by: Javier Martinez Canillas <javierm@redhat.com> -- Best regards, Javier Martinez Canillas Linux Engineering Red Hat
next prev parent reply other threads:[~2022-04-13 9:16 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-04-13 8:21 [PATCH] fbcon: Fix delayed takeover locking Daniel Vetter 2022-04-13 8:21 ` [Intel-gfx] " Daniel Vetter 2022-04-13 9:16 ` Javier Martinez Canillas [this message] 2022-04-13 9:16 ` Javier Martinez Canillas 2022-04-13 9:21 ` Daniel Vetter 2022-04-13 9:21 ` [Intel-gfx] " Daniel Vetter 2022-04-13 9:31 ` Javier Martinez Canillas 2022-04-13 9:31 ` [Intel-gfx] " Javier Martinez Canillas 2022-04-13 9:25 ` Daniel Vetter 2022-04-13 9:25 ` [Intel-gfx] " Daniel Vetter 2022-04-13 15:20 ` Nathan Chancellor 2022-04-13 15:20 ` [Intel-gfx] " Nathan Chancellor 2022-04-13 20:50 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for " Patchwork 2022-04-13 21:12 ` [Intel-gfx] ✓ Fi.CI.BAT: success " Patchwork 2022-04-13 23:13 ` [Intel-gfx] ✗ Fi.CI.IGT: failure " Patchwork
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