From: Jan Kara <jack@suse.cz>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zijlstra <peterz@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Sebastian Siewior <bigeasy@linutronix.de>,
Theodore Tso <tytso@mit.edu>, Julia Cartwright <julia@ni.com>,
Jan Kara <jack@suse.com>,
linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [patch 3/4] fs/buffer: Substitute BH_Uptodate_Lock for RT and bit spinlock debugging
Date: Wed, 31 Jul 2019 16:47:32 +0200 [thread overview]
Message-ID: <20190731144732.GH15806@quack2.suse.cz> (raw)
In-Reply-To: <20190730120321.393759046@linutronix.de>
On Tue 30-07-19 13:24:55, Thomas Gleixner wrote:
> Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable
> preemption, which is undesired for latency reasons and breaks when regular
> spinlocks are taken within the bit_spinlock locked region because regular
> spinlocks are converted to 'sleeping spinlocks' on RT.
>
> Substitute the BH_Uptodate_Lock bit spinlock with a regular spinlock for
> PREEMPT_RT enabled kernels.
>
> Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With
> the spinlock substitution in place, they can be exposed via
> CONFIG_DEBUG_BIT_SPINLOCKS.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Theodore Ts'o" <tytso@mit.edu>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: linux-fsdevel@vger.kernel.org
Looks good to me. You can add:
Reviewed-by: Jan Kara <jack@suse.cz>
Honza
> ---
> fs/buffer.c | 1 +
> include/linux/buffer_head.h | 31 +++++++++++++++++++++++++++++++
> 2 files changed, 32 insertions(+)
>
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3360,6 +3360,7 @@ struct buffer_head *alloc_buffer_head(gf
> struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
> if (ret) {
> INIT_LIST_HEAD(&ret->b_assoc_buffers);
> + buffer_head_init_locks(ret);
> preempt_disable();
> __this_cpu_inc(bh_accounting.nr);
> recalc_bh_state();
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -76,8 +76,35 @@ struct buffer_head {
> struct address_space *b_assoc_map; /* mapping this buffer is
> associated with */
> atomic_t b_count; /* users using this buffer_head */
> +
> +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS)
> + spinlock_t b_uptodate_lock;
> +#endif
> };
>
> +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS)
> +
> +static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&bh->b_uptodate_lock, flags);
> + return flags;
> +}
> +
> +static inline void
> +bh_uptodate_unlock_irqrestore(struct buffer_head *bh, unsigned long flags)
> +{
> + spin_unlock_irqrestore(&bh->b_uptodate_lock, flags);
> +}
> +
> +static inline void buffer_head_init_locks(struct buffer_head *bh)
> +{
> + spin_lock_init(&bh->b_uptodate_lock);
> +}
> +
> +#else /* PREEMPT_RT || DEBUG_BIT_SPINLOCKS */
> +
> static inline unsigned long bh_uptodate_lock_irqsave(struct buffer_head *bh)
> {
> unsigned long flags;
> @@ -94,6 +121,10 @@ bh_uptodate_unlock_irqrestore(struct buf
> local_irq_restore(flags);
> }
>
> +static inline void buffer_head_init_locks(struct buffer_head *bh) { }
> +
> +#endif /* !PREEMPT_RT && !DEBUG_BIT_SPINLOCKS */
> +
> /*
> * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
> * and buffer_foo() functions.
>
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-07-31 14:47 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 11:24 [patch 0/4] fs: Substitute bit-spinlocks for PREEMPT_RT and debugging Thomas Gleixner
2019-07-30 11:24 ` [patch 1/4] locking/lockdep: Add Kconfig option for bit spinlocks Thomas Gleixner
2019-07-30 11:24 ` [patch 2/4] fs/buffer: Move BH_Uptodate_Lock locking into wrapper functions Thomas Gleixner
2019-07-31 14:46 ` Jan Kara
2019-07-31 22:27 ` Thomas Gleixner
2019-07-30 11:24 ` [patch 3/4] fs/buffer: Substitute BH_Uptodate_Lock for RT and bit spinlock debugging Thomas Gleixner
2019-07-31 14:47 ` Jan Kara [this message]
2019-07-30 11:24 ` [patch 4/4] fs: jbd/jbd2: Substitute BH locks for RT and lock debugging Thomas Gleixner
2019-07-31 15:48 ` Jan Kara
2019-07-31 19:40 ` Thomas Gleixner
2019-08-01 8:44 ` Jan Kara
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190731144732.GH15806@quack2.suse.cz \
--to=jack@suse.cz \
--cc=anna-maria@linutronix.de \
--cc=bigeasy@linutronix.de \
--cc=jack@suse.com \
--cc=julia@ni.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
--cc=tytso@mit.edu \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).