From: Peter Zijlstra <peterz@infradead.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
John Ogness <john.ogness@linutronix.de>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t
Date: Wed, 9 Dec 2020 13:29:09 +0100 [thread overview]
Message-ID: <20201209122909.GL2414@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <X9C09N5r4sGdel+h@jagdpanzerIV.localdomain>
On Wed, Dec 09, 2020 at 08:28:52PM +0900, Sergey Senozhatsky wrote:
> On (20/12/09 12:00), Peter Zijlstra wrote:
> > > So another potential re-entry path is
> > >
> > > atomic_foo()
> > > spin_lock_irqsave(ATOMIC_HASH(v), flags)
> > > printk()
> > > prb()
> > > atomic_foo()
> > > spin_lock_irqsave(ATOMIC_HASH(v), flags)
> > >
> > > which can deadlock, in theory, if both atomics HASH to the same
> > > key (same spin_lock).
> >
> > Yep, but see the 'mostly' in the 'they mostly work'. Given the
> > limitiations of these architectures there's really only so much you can
> > do.
>
> Right, agreed.
>
> Nevertheless TIL that lockless printk buffer is not always lockless.
> Perhaps, people that work with those archs need to also know this.
Last time I broke them, they were aware they're 'special' and IIRC
they're mostly just limping along on prayers.
> I haven't checked all the archs, but if, somehow, (IF) some of them
> can panic the system with the atomic hash entries locked, then on
> those archs new printk may not be able to flush-on-panic. Because
> while printk iterates logbuf it may HASH to the atomic hash table
> entry, that will never be unlocked. So there are some changes in
> atomic/printk department on those archs.
Yeah, so I wouldn't put too much effort into thinking about it.
Hopefully we can eventually delete these architectures and really forget
they exist.
next prev parent reply other threads:[~2020-12-09 12:30 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-01 20:53 [PATCH next v2 0/3] printk: remove logbuf_lock John Ogness
2020-12-01 20:53 ` [PATCH next v2 1/3] printk: inline log_output(),log_store() in vprintk_store() John Ogness
2020-12-03 15:57 ` Petr Mladek
2020-12-03 16:25 ` John Ogness
2020-12-04 6:13 ` Sergey Senozhatsky
2020-12-04 8:26 ` Petr Mladek
2020-12-01 20:53 ` [PATCH next v2 2/3] printk: change @clear_seq to atomic64_t John Ogness
2020-12-04 9:12 ` Petr Mladek
2020-12-06 20:23 ` John Ogness
2020-12-07 9:34 ` Peter Zijlstra
2020-12-07 10:03 ` John Ogness
2020-12-07 12:56 ` Peter Zijlstra
2020-12-07 12:56 ` Petr Mladek
2020-12-07 16:46 ` David Laight
2020-12-08 20:34 ` Sergey Senozhatsky
2020-12-08 22:30 ` John Ogness
2020-12-09 1:04 ` Sergey Senozhatsky
2020-12-09 8:16 ` Peter Zijlstra
2020-12-09 9:22 ` Sergey Senozhatsky
2020-12-09 10:46 ` Sergey Senozhatsky
2020-12-09 11:00 ` Peter Zijlstra
2020-12-09 11:28 ` Sergey Senozhatsky
2020-12-09 12:29 ` Peter Zijlstra [this message]
2020-12-09 8:07 ` Peter Zijlstra
2020-12-01 20:53 ` [PATCH next v2 3/3] printk: remove logbuf_lock, add syslog_lock John Ogness
2020-12-04 6:41 ` Sergey Senozhatsky
2020-12-06 20:44 ` John Ogness
2020-12-04 15:52 ` devkmsg: was " Petr Mladek
2020-12-06 20:51 ` John Ogness
2020-12-07 9:56 ` Petr Mladek
2020-12-04 15:57 ` syslog: was: " Petr Mladek
2020-12-06 21:06 ` John Ogness
2020-12-07 10:01 ` Petr Mladek
2020-12-04 16:10 ` recursion handling: " Petr Mladek
2020-12-05 4:25 ` Sergey Senozhatsky
2020-12-06 22:08 ` John Ogness
2020-12-05 9:41 ` Sergey Senozhatsky
2020-12-06 22:17 ` John Ogness
2020-12-06 21:44 ` John Ogness
2020-12-07 11:17 ` Petr Mladek
2020-12-04 16:15 ` vprintk_store: was: " Petr Mladek
2020-12-06 22:30 ` John Ogness
2020-12-07 12:46 ` Petr Mladek
2020-12-04 16:19 ` consoles: " Petr Mladek
2020-12-05 4:39 ` Sergey Senozhatsky
2020-12-07 9:50 ` Petr Mladek
2020-12-08 20:51 ` Sergey Senozhatsky
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