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console_unblank() does this too (called in both places right after), and with a lot more confidence inspiring approach to locking. Reconstructing this story is very strange: Inb61312d353("oops handling: ensure that any oops is flushed to the mtdoops console") it is claimed that a printk(" "); flushed out the console buffer, which was removed ine3e8a75d2a("[PATCH] Extract and use wake_up_klogd()"). In todays kernels this is done way earlier in console_flush_on_panic with some really nasty tricks. I didn't bother to fully reconstruct this all, least because the call to bust_spinlock(0); gets moved every few years, depending upon how the wind blows (or well, who screamed loudest about the various issue each call site caused). Before that commit the only calls to console_unblank() where in s390 arch code. The other side here is the console->unblank callback, which was introduced in 2.1.31 for the vt driver. Which predates the console_unblank() function by a lot, which was added (without users) in 2.4.14.3. So pretty much impossible to guess at any motivation here. Also afaict the vt driver is the only (and always was the only) console driver implementing the unblank callback, so no idea why a call to console_unblank() was added for the mtdooops driver - the action actually flushing out the console buffers is done from console_unlock() only. Note that as prep for the s390 users the locking was adjusted in 2.5.22 (I couldn't figure out how to properly reference the BK commit from the historical git trees) from a normal semaphore to a trylock. Note that a copy of the direct unblank_screen() call was added to panic() inc7c3f05e34("panic: avoid deadlocks in re-entrant console drivers"), which partially inlined the bust_spinlocks(0); call. Long story short, I have no idea why the direct call to unblank_screen survived for so long (the infrastructure to do it properly existed for years), nor why it wasn't removed when the console_unblank() call was finally added. But it makes a ton more sense to finally do that than not - it's just better encapsulation to go through the console functions instead of doing a direct call, so let's dare. Plus it really does not make much sense to call the only unblank implementation there is twice, once without, and once with appropriate locking. Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jirislaby@kernel.org> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> Cc: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Xuezhi Zhang <zhangxuezhi1@coolpad.com> Cc: Yangxi Xiang <xyangxi5@gmail.com> Cc: nick black <dankamongmen@gmail.com> Cc: Petr Mladek <pmladek@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com> Cc: Marco Elver <elver@google.com> Cc: John Ogness <john.ogness@linutronix.de> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: David Gow <davidgow@google.com> Cc: tangmeng <tangmeng@uniontech.com> Cc: Tiezhu Yang <yangtiezhu@loongson.cn> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Petr Mladek <pmladek@suse.com> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Link: https://lore.kernel.org/r/20220830145004.430545-1-daniel.vetter@ffwll.ch Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
29 lines
632 B
C
29 lines
632 B
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* lib/bust_spinlocks.c
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*
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* Provides a minimal bust_spinlocks for architectures which don't
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* have one of their own.
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*
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* bust_spinlocks() clears any spinlocks which would prevent oops, die(), BUG()
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* and panic() information from reaching the user.
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*/
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#include <linux/kernel.h>
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#include <linux/printk.h>
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#include <linux/spinlock.h>
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#include <linux/tty.h>
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#include <linux/wait.h>
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#include <linux/vt_kern.h>
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#include <linux/console.h>
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void bust_spinlocks(int yes)
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{
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if (yes) {
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++oops_in_progress;
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} else {
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console_unblank();
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if (--oops_in_progress == 0)
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wake_up_klogd();
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}
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}
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