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Date: Thu, 8 Aug 2019 09:54:03 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Christoph Hellwig <hch@...radead.org>
cc: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Sebastian Siewior <bigeasy@...utronix.de>,
Anna-Maria Gleixner <anna-maria@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>,
Julia Cartwright <julia@...com>, Jan Kara <jack@...e.cz>,
Theodore Tso <tytso@....edu>,
Matthew Wilcox <willy@...radead.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
Jan Kara <jack@...e.com>, Mark Fasheh <mark@...heh.com>,
Joseph Qi <joseph.qi@...ux.alibaba.com>,
Joel Becker <jlbec@...lplan.org>
Subject: Re: [patch V2 0/7] fs: Substitute bit-spinlocks for PREEMPT_RT and
debugging
On Thu, 8 Aug 2019, Christoph Hellwig wrote:
> On Thu, Aug 08, 2019 at 09:02:47AM +0200, Thomas Gleixner wrote:
> > > > mm/slub.c: bit_spin_lock(PG_locked, &page->flags);
> > >
> > > One caller ouf of a gazillion that spins on the page lock instead of
> > > sleepign on it like everyone else. That should not have passed your
> > > smell test to start with :)
> >
> > I surely stared at it, but that cannot sleep. It's in the middle of a
> > preempt and interrupt disabled region and used on architectures which do
> > not support CMPXCHG_DOUBLE and ALIGNED_STRUCT_PAGE ...
>
> I know. But the problem here is that normally PG_locked is used together
> with wait_on_page_bit_*, but this one instances uses the bit spinlock
> helpers. This is the equivalent of calling spin_lock on a struct mutex
> rather than having a mutex_lock_spin helper for this case.
Yes, I know :(
> Does SLUB work on -rt at all?
It's the only allocator we support with a few tweaks :)
Thanks,
tglx
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