From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hans de Goede Date: Thu, 09 Aug 2018 11:28:25 +0000 Subject: Re: [PATCH fix for 4.19] fbcon: Do not takeover the console from atomic context Message-Id: <1e8d458b-98c1-57e8-da77-4f17eecd7360@redhat.com> List-Id: References: <20180806155416.15752-1-hdegoede@redhat.com> <1667652.5c9CXM81DN@amdc3058> In-Reply-To: <1667652.5c9CXM81DN@amdc3058> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Bartlomiej Zolnierkiewicz Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org Hi, On 09-08-18 12:03, Bartlomiej Zolnierkiewicz wrote: > On Monday, August 06, 2018 05:54:16 PM Hans de Goede wrote: >> Taking over the console involves allocating mem with GFP_KERNEL, talking >> to drm drivers, etc. So this should not be done from an atomic context. >> >> But the console-output trigger deferred console takeover may happen from an >> atomic context, which leads to "BUG: sleeping function called from invalid >> context" errors. >> >> This commit fixes these errors by doing the deferred takeover from a >> workqueue when the notifier runs from an atomic context. >> >> Signed-off-by: Hans de Goede > > checkpatch.pl complains about in_atomic use: > > ERROR: do not use in_atomic in drivers > #51: FILE: drivers/video/fbdev/core/fbcon.c:3623: > + if (in_atomic() || irqs_disabled()) { > > please also see the comment in preempt.h: > > /* > * Are we running in atomic context? WARNING: this macro cannot > * always detect atomic context; in particular, it cannot know about > * held spinlocks in non-preemptible kernels. Thus it should not be > * used in the general case to determine whether sleeping is possible. > * Do not use in_atomic() in driver code. > */ > #define in_atomic() (preempt_count() != 0) > > Therefore please explain why it is fine to use in_atomic in fbcon's case. Ok I will send a v2 which adds a comment why we need to use in_atomic here. Regards, Hans > >> --- >> drivers/video/fbdev/core/fbcon.c | 21 +++++++++++++++++++-- >> 1 file changed, 19 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c >> index ef8b2d0b7071..4e5997d53fc4 100644 >> --- a/drivers/video/fbdev/core/fbcon.c >> +++ b/drivers/video/fbdev/core/fbcon.c >> @@ -3592,7 +3592,20 @@ static int fbcon_init_device(void) >> } >> >> #ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >> +static void fbcon_register_existing_fbs(struct work_struct *work) >> +{ >> + int i; >> + >> + console_lock(); >> + >> + for_each_registered_fb(i) >> + fbcon_fb_registered(registered_fb[i]); >> + >> + console_unlock(); >> +} >> + >> static struct notifier_block fbcon_output_nb; >> +static DECLARE_WORK(fbcon_deferred_takeover_work, fbcon_register_existing_fbs); >> >> static int fbcon_output_notifier(struct notifier_block *nb, >> unsigned long action, void *data) >> @@ -3607,8 +3620,12 @@ static int fbcon_output_notifier(struct notifier_block *nb, >> deferred_takeover = false; >> logo_shown = FBCON_LOGO_DONTSHOW; >> >> - for_each_registered_fb(i) >> - fbcon_fb_registered(registered_fb[i]); >> + if (in_atomic() || irqs_disabled()) { >> + schedule_work(&fbcon_deferred_takeover_work); >> + } else { >> + for_each_registered_fb(i) >> + fbcon_fb_registered(registered_fb[i]); >> + } >> >> return NOTIFY_OK; >> } > > Best regards, > -- > Bartlomiej Zolnierkiewicz > Samsung R&D Institute Poland > Samsung Electronics >