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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Daniel Vetter <daniel.vetter@intel.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Hans de Goede <hdegoede@redhat.com>,
	Yisheng Xie <ysxie@foxmail.com>
Subject: [PATCH 31/33] fbcon: Document what I learned about fbcon locking
Date: Fri, 24 May 2019 10:53:52 +0200	[thread overview]
Message-ID: <20190524085354.27411-32-daniel.vetter@ffwll.ch> (raw)
In-Reply-To: <20190524085354.27411-1-daniel.vetter@ffwll.ch>

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 6a4bbb8407c0..8444d5151c2d 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -88,6 +88,25 @@
 #  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 */
-- 
2.20.1


  parent reply	other threads:[~2019-05-24  8:54 UTC|newest]

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-24  8:53 [PATCH 00/33] fbcon notifier begone! Daniel Vetter
2019-05-24  8:53 ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 01/33] dummycon: Sprinkle locking checks Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 02/33] fbdev: locking check for fb_set_suspend Daniel Vetter
2019-05-24  8:53 ` [PATCH 03/33] vt: might_sleep() annotation for do_blank_screen Daniel Vetter
2019-05-24  8:53 ` [PATCH 04/33] vt: More locking checks Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-27  7:08   ` Daniel Vetter
2019-05-27  7:08     ` Daniel Vetter
2019-05-27  7:22     ` Greg Kroah-Hartman
2019-05-24  8:53 ` [PATCH 05/33] fbdev/sa1100fb: Remove dead code Daniel Vetter
2019-05-24  8:53 ` [PATCH 06/33] fbdev/cyber2000: Remove struct display Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 07/33] fbdev/aty128fb: Remove dead code Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 08/33] fbcon: s/struct display/struct fbcon_display/ Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 09/33] fbcon: Remove fbcon_has_exited Daniel Vetter
2019-05-25 15:38   ` Sam Ravnborg
2019-05-25 15:38     ` Sam Ravnborg
2019-05-27  6:10     ` Daniel Vetter
2019-05-27  6:10       ` Daniel Vetter
2019-05-27  6:51       ` Sam Ravnborg
2019-05-27  6:51         ` Sam Ravnborg
2019-05-24  8:53 ` [PATCH 10/33] fbcon: call fbcon_fb_(un)registered directly Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 11/33] fbdev/sh_mobile: remove sh_mobile_lcdc_display_notify Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-25 15:01   ` Sam Ravnborg
2019-05-25 15:01     ` Sam Ravnborg
2019-05-27  6:13     ` Daniel Vetter
2019-05-27  6:52       ` Sam Ravnborg
2019-05-24  8:53 ` [PATCH 12/33] fbdev/omap: sysfs files can't disappear before the device is gone Daniel Vetter
2019-05-24  8:53 ` [PATCH 13/33] fbdev: " Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 14/33] staging/olpc: lock_fb_info can't fail Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-27  7:10   ` Daniel Vetter
2019-05-27  7:22     ` Greg KH
2019-05-27  7:22       ` Greg KH
2019-05-24  8:53 ` [PATCH 15/33] fbdev/atyfb: " Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 16/33] fbdev: lock_fb_info cannot fail Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 17/33] fbcon: call fbcon_fb_bind directly Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 18/33] fbdev: make unregister/unlink functions not fail Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 19/33] fbdev: unify unlink_framebuffer paths Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 20/33] fbdev/sh_mob: Remove fb notifier callback Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 21/33] fbdev: directly call fbcon_suspended/resumed Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 22/33] fbcon: Call fbcon_mode_deleted/new_modelist directly Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 23/33] fbdev: Call fbcon_get_requirement directly Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 24/33] Revert "backlight/fbcon: Add FB_EVENT_CONBLANK" Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24 13:14   ` Daniel Thompson
2019-05-24 13:14     ` Daniel Thompson
2019-05-24 13:14     ` Daniel Thompson
2019-05-24 15:28     ` Daniel Vetter
2019-05-24 15:28       ` Daniel Vetter
2019-05-27 10:59       ` Bartlomiej Zolnierkiewicz
2019-05-27 10:59         ` Bartlomiej Zolnierkiewicz
2019-05-24  8:53 ` [PATCH 25/33] fbmem: pull fbcon_fb_blanked out of fb_blank Daniel Vetter
2019-05-25 17:00   ` Sam Ravnborg
2019-05-25 17:00     ` Sam Ravnborg
2019-05-24  8:53 ` [PATCH 26/33] fbdev: remove FBINFO_MISC_USEREVENT around fb_blank Daniel Vetter
2019-05-24  8:53 ` [PATCH 27/33] fb: Flatten control flow in fb_set_var Daniel Vetter
2019-05-24  8:53 ` [PATCH 28/33] fbcon: replace FB_EVENT_MODE_CHANGE/_ALL with direct calls Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 29/33] vgaswitcheroo: call fbcon_remap_all directly Daniel Vetter
2019-05-24  8:53   ` Daniel Vetter
2019-05-24  8:53 ` [PATCH 30/33] fbcon: Call con2fb_map functions directly Daniel Vetter
2019-05-24  8:53 ` Daniel Vetter [this message]
2019-05-24  8:53 ` [PATCH 32/33] staging/olpc_dcon: Add drm conversion to TODO Daniel Vetter
2019-05-27  7:11   ` Daniel Vetter
2019-05-27  7:11     ` Daniel Vetter
2019-05-27  7:22     ` Greg KH
2019-05-24  8:53 ` [PATCH 33/33] backlight: simplify lcd notifier Daniel Vetter
2019-05-24 11:03 ` ✗ Fi.CI.CHECKPATCH: warning for fbcon notifier begone! (rev3) Patchwork
2019-05-24 11:18 ` ✗ Fi.CI.SPARSE: " Patchwork
2019-05-24 11:23 ` ✓ Fi.CI.BAT: success " Patchwork
2019-05-25 17:19 ` [PATCH 00/33] fbcon notifier begone! Sam Ravnborg
2019-05-27  7:17   ` Daniel Vetter
2019-05-27 11:56     ` Daniel Vetter
2019-05-25 17:24 ` ✗ Fi.CI.IGT: failure for fbcon notifier begone! (rev3) Patchwork
2019-05-26 15:34 ` ✗ Fi.CI.CHECKPATCH: warning for fbcon notifier begone! (rev4) Patchwork
2019-05-26 15:49 ` ✗ Fi.CI.SPARSE: " Patchwork
2019-05-26 15:53 ` ✓ Fi.CI.BAT: success " Patchwork
2019-05-27 11:02 ` ✓ Fi.CI.IGT: " Patchwork
2019-05-28  9:02 [PATCH 00/33] fbcon notifier begone v3! Daniel Vetter
2019-05-28  9:03 ` [PATCH 31/33] fbcon: Document what I learned about fbcon locking Daniel Vetter
2019-05-28  9:03   ` Daniel Vetter

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