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From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>,
	DRI Development <dri-devel@lists.freedesktop.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Yisheng Xie <ysxie@foxmail.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH 32/33] fbcon: Document what I learned about fbcon locking
Date: Tue, 21 May 2019 13:13:58 +0200	[thread overview]
Message-ID: <4ce4193c-5140-a833-28d9-72b3d673da73@linux.intel.com> (raw)
In-Reply-To: <20190520082216.26273-33-daniel.vetter@ffwll.ch>

Op 20-05-2019 om 10:22 schreef Daniel Vetter:
> It's not pretty.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Yisheng Xie <ysxie@foxmail.com>
> ---
>  drivers/video/fbdev/core/fbcon.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index b40b56702c61..cbbcf7a795f2 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -87,6 +87,25 @@
>  #  define DPRINTK(fmt, args...)
>  #endif
>  
> +/*
> + * FIXME: Locking
> + *
> + * - fbcon state itself is protected by the console_lock, and the code does a
> + *   pretty good job at making sure that lock is held everywhere it's needed.
> + *
> + * - access to the registered_fb array is entirely unprotected. This should use
> + *   proper object lifetime handling, i.e. get/put_fb_info. This also means
> + *   switching from indices to proper pointers for fb_info everywhere.
> + *
> + * - fbcon doesn't bother with fb_lock/unlock at all. This is buggy, since it
> + *   means concurrent access to the same fbdev from both fbcon and userspace
> + *   will blow up. To fix this all fbcon calls from fbmem.c need to be moved out
> + *   of fb_lock/unlock protected sections, since otherwise we'll recurse and
> + *   deadlock eventually. Aside: Due to these deadlock issues the fbdev code in
> + *   fbmem.c cannot use locking asserts, and there's lots of callers which get
> + *   the rules wrong, e.g. fbsysfs.c entirely missed fb_lock/unlock calls too.
> + */
> +
>  enum {
>  	FBCON_LOGO_CANSHOW	= -1,	/* the logo can be shown */
>  	FBCON_LOGO_DRAW		= -2,	/* draw the logo to a console */

I did a casual review, so for whole series with the small nitpicks I had, and any feedback by others, kbuild and the arm mess being fixed up:

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

However, according to reviewer's statement of oversight:

While I have reviewed the patch and believe it to be sound, I do not (unless explicitly stated elsewhere)
make any warranties or guarantees that it will achieve its stated purpose or function properly in any given situation.

:)

~Maarten


  reply	other threads:[~2019-05-21 11:14 UTC|newest]

Thread overview: 112+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20  8:21 [PATCH 00/33] fbcon notifier begone! Daniel Vetter
2019-05-20  8:21 ` [PATCH 01/33] dummycon: Sprinkle locking checks Daniel Vetter
2019-05-20  8:21 ` [PATCH 02/33] fbdev: locking check for fb_set_suspend Daniel Vetter
2019-05-20  8:21 ` [PATCH 03/33] vt: might_sleep() annotation for do_blank_screen Daniel Vetter
2019-05-20  8:21 ` [PATCH 04/33] vt: More locking checks Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 05/33] fbdev/sa1100fb: Remove dead code Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 06/33] fbdev/cyber2000: Remove struct display Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 07/33] fbdev/aty128fb: Remove dead code Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 08/33] fbcon: s/struct display/struct fbcon_display/ Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 09/33] fbcon: Remove fbcon_has_exited Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-21 14:23   ` [PATCH] " Daniel Vetter
2019-05-22 10:04     ` Bartlomiej Zolnierkiewicz
2019-05-22 10:04       ` Bartlomiej Zolnierkiewicz
2019-05-22 10:38       ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 10/33] fbcon: call fbcon_fb_(un)registered directly Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:33   ` Thomas Zimmermann
2019-05-20  8:33     ` Thomas Zimmermann
2019-05-20  8:37     ` Thomas Zimmermann
2019-05-20  8:37       ` Thomas Zimmermann
2019-05-21 15:09       ` Daniel Vetter
2019-05-21 15:09         ` Daniel Vetter
2019-05-20 17:08   ` Sam Ravnborg
2019-05-20 17:08     ` Sam Ravnborg
2019-05-20 17:08     ` Sam Ravnborg
2019-05-20 17:25     ` Daniel Vetter
2019-05-20 17:25       ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 11/33] fbdev/sh_mobile: remove sh_mobile_lcdc_display_notify Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  9:04   ` Geert Uytterhoeven
2019-05-20  8:21 ` [PATCH 12/33] fbdev/omap: sysfs files can't disappear before the device is gone Daniel Vetter
2019-05-20  8:21 ` [PATCH 13/33] fbdev: " Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 14/33] staging/olpc: lock_fb_info can't fail Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 15/33] fbdev/atyfb: " Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:21 ` [PATCH 16/33] fbdev: lock_fb_info cannot fail Daniel Vetter
2019-05-20  8:21   ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 17/33] fbcon: call fbcon_fb_bind directly Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 18/33] fbdev: make unregister/unlink functions not fail Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20 19:08   ` [Intel-gfx] " kbuild test robot
2019-05-20 19:08     ` kbuild test robot
2019-05-20 19:08     ` kbuild test robot
2019-05-20 19:25   ` kbuild test robot
2019-05-20 19:25     ` kbuild test robot
2019-05-20 19:25     ` [Intel-gfx] " kbuild test robot
2019-05-20 21:45   ` kbuild test robot
2019-05-20 21:45     ` kbuild test robot
2019-05-20 21:45     ` kbuild test robot
2019-05-20  8:22 ` [PATCH 19/33] fbdev: unify unlink_framebufer paths Daniel Vetter
2019-05-21 10:52   ` Maarten Lankhorst
2019-05-20  8:22 ` [PATCH 20/33] fbdev/sh_mob: Remove fb notifier callback Daniel Vetter
2019-05-20  9:05   ` Geert Uytterhoeven
2019-05-20  9:19     ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 21/33] fbdev: directly call fbcon_suspended/resumed Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20 19:24   ` kbuild test robot
2019-05-20 19:24     ` kbuild test robot
2019-05-20 19:24     ` kbuild test robot
2019-05-20  8:22 ` [PATCH 22/33] fbcon: Call fbcon_mode_deleted/new_modelist directly Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 23/33] fbdev: Call fbcon_get_requirement directly Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 24/33] Revert "backlight/fbcon: Add FB_EVENT_CONBLANK" Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 25/33] fbcon: directly call fbcon_fb_blanked Daniel Vetter
2019-05-20  8:22 ` [PATCH 26/33] fbmem: pull fbcon_fb_blanked out of fb_blank Daniel Vetter
2019-05-20  8:22 ` [PATCH 27/33] fbdev: remove FBINFO_MISC_USEREVENT around fb_blank Daniel Vetter
2019-05-20 17:20   ` Sam Ravnborg
2019-05-20 17:20     ` Sam Ravnborg
2019-05-20 17:29     ` Daniel Vetter
2019-05-20 17:29       ` Daniel Vetter
2019-05-20 17:53       ` Sam Ravnborg
2019-05-20  8:22 ` [PATCH 28/33] fb: Flatten control flow in fb_set_var Daniel Vetter
2019-05-20  8:22 ` [PATCH 29/33] fbcon: replace FB_EVENT_MODE_CHANGE/_ALL with direct calls Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-21 10:56   ` Maarten Lankhorst
2019-05-21 10:56     ` Maarten Lankhorst
2019-05-21 12:42     ` Daniel Vetter
2019-05-21 12:42       ` Daniel Vetter
2019-05-21 12:42       ` Daniel Vetter
2019-05-20  8:22 ` [PATCH 30/33] vgaswitcheroo: call fbcon_remap_all directly Daniel Vetter
2019-05-20  8:22   ` Daniel Vetter
2019-05-20  8:37   ` Lukas Wunner
2019-05-20  8:37     ` Lukas Wunner
2019-05-20  8:22 ` [PATCH 31/33] fbcon: Call con2fb_map functions directly Daniel Vetter
2019-05-20 19:28   ` [Intel-gfx] " kbuild test robot
2019-05-20 19:28     ` kbuild test robot
2019-05-20 19:34   ` [Intel-gfx] " kbuild test robot
2019-05-20 19:34     ` kbuild test robot
2019-05-20  8:22 ` [PATCH 32/33] fbcon: Document what I learned about fbcon locking Daniel Vetter
2019-05-21 11:13   ` Maarten Lankhorst [this message]
2019-05-20  8:22 ` [PATCH 33/33] staging/olpc_dcon: Add drm conversion to TODO Daniel Vetter
2019-05-20  8:30 ` ✗ Fi.CI.CHECKPATCH: warning for fbcon notifier begone! Patchwork
2019-05-20  8:41 ` ✗ Fi.CI.BAT: failure " Patchwork
2019-05-20  8:44 ` ✗ Fi.CI.SPARSE: warning " Patchwork
2019-05-21 17:08 ` ✗ Fi.CI.CHECKPATCH: warning for fbcon notifier begone! (rev2) Patchwork
2019-05-21 17:22 ` ✗ Fi.CI.SPARSE: " Patchwork
2019-05-21 17:29 ` ✗ Fi.CI.BAT: failure " Patchwork
2019-05-22  8:15 ` ✓ Fi.CI.BAT: success " Patchwork
2019-05-22 18:43 ` ✓ Fi.CI.IGT: " Patchwork

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