From: Joel Fernandes <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Bjorn Helgaas <bhelgaas@google.com>,
Borislav Petkov <bp@alien8.de>,
c0d1n61at3@gmail.com, "David S. Miller" <davem@davemloft.net>,
edumazet@google.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Josh Triplett <josh@joshtriplett.org>,
keescook@chromium.org, kernel-hardening@lists.openwall.com,
kernel-team@android.com, Lai Jiangshan <jiangshanlai@gmail.com>,
Len Brown <lenb@kernel.org>,
linux-acpi@vger.kernel.org, linux-doc@vger.kernel.org,
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Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
neilb@suse.com, netdev@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
Pavel Machek <pavel@ucw.cz>,
peterz@infradead.org, "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
rcu@vger.kernel.org, Steven Rostedt <rostedt@goodmis.org>,
Tejun Heo <tj@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
will@kernel.org,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>
Subject: Re: [PATCH v2 3/9] rcu/sync: Remove custom check for reader-section
Date: Fri, 12 Jul 2019 17:35:59 -0400 [thread overview]
Message-ID: <20190712213559.GA175138@google.com> (raw)
In-Reply-To: <20190712170024.111093-4-joel@joelfernandes.org>
On Fri, Jul 12, 2019 at 01:00:18PM -0400, Joel Fernandes (Google) wrote:
> The rcu/sync code was doing its own check whether we are in a reader
> section. With RCU consolidating flavors and the generic helper added in
> this series, this is no longer need. We can just use the generic helper
> and it results in a nice cleanup.
>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Hi Oleg,
Slightly unrelated to the patch,
I tried hard to understand this comment below in percpu_down_read() but no dice.
I do understand how rcu sync and percpu rwsem works, however the comment
below didn't make much sense to me. For one, there's no readers_fast anymore
so I did not follow what readers_fast means. Could the comment be updated to
reflect latest changes?
Also could you help understand how is a writer not able to change
sem->state and count the per-cpu read counters at the same time as the
comment tries to say?
/*
* We are in an RCU-sched read-side critical section, so the writer
* cannot both change sem->state from readers_fast and start checking
* counters while we are here. So if we see !sem->state, we know that
* the writer won't be checking until we're past the preempt_enable()
* and that once the synchronize_rcu() is done, the writer will see
* anything we did within this RCU-sched read-size critical section.
*/
Also,
I guess we could get rid of all of the gp_ops struct stuff now that since all
the callbacks are the same now. I will post that as a follow-up patch to this
series.
thanks!
- Joel
> ---
> Please note: Only build and boot tested this particular patch so far.
>
> include/linux/rcu_sync.h | 5 ++---
> kernel/rcu/sync.c | 22 ----------------------
> 2 files changed, 2 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
> index 6fc53a1345b3..c954f1efc919 100644
> --- a/include/linux/rcu_sync.h
> +++ b/include/linux/rcu_sync.h
> @@ -39,9 +39,8 @@ extern void rcu_sync_lockdep_assert(struct rcu_sync *);
> */
> static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
> {
> -#ifdef CONFIG_PROVE_RCU
> - rcu_sync_lockdep_assert(rsp);
> -#endif
> + RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),
> + "suspicious rcu_sync_is_idle() usage");
> return !rsp->gp_state; /* GP_IDLE */
> }
>
> diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
> index a8304d90573f..535e02601f56 100644
> --- a/kernel/rcu/sync.c
> +++ b/kernel/rcu/sync.c
> @@ -10,37 +10,25 @@
> #include <linux/rcu_sync.h>
> #include <linux/sched.h>
>
> -#ifdef CONFIG_PROVE_RCU
> -#define __INIT_HELD(func) .held = func,
> -#else
> -#define __INIT_HELD(func)
> -#endif
> -
> static const struct {
> void (*sync)(void);
> void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
> void (*wait)(void);
> -#ifdef CONFIG_PROVE_RCU
> - int (*held)(void);
> -#endif
> } gp_ops[] = {
> [RCU_SYNC] = {
> .sync = synchronize_rcu,
> .call = call_rcu,
> .wait = rcu_barrier,
> - __INIT_HELD(rcu_read_lock_held)
> },
> [RCU_SCHED_SYNC] = {
> .sync = synchronize_rcu,
> .call = call_rcu,
> .wait = rcu_barrier,
> - __INIT_HELD(rcu_read_lock_sched_held)
> },
> [RCU_BH_SYNC] = {
> .sync = synchronize_rcu,
> .call = call_rcu,
> .wait = rcu_barrier,
> - __INIT_HELD(rcu_read_lock_bh_held)
> },
> };
>
> @@ -49,16 +37,6 @@ enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
>
> #define rss_lock gp_wait.lock
>
> -#ifdef CONFIG_PROVE_RCU
> -void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
> -{
> - RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
> - "suspicious rcu_sync_is_idle() usage");
> -}
> -
> -EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert);
> -#endif
> -
> /**
> * rcu_sync_init() - Initialize an rcu_sync structure
> * @rsp: Pointer to rcu_sync structure to be initialized
> --
> 2.22.0.510.g264f2c817a-goog
>
next prev parent reply other threads:[~2019-07-12 21:36 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-12 17:00 [PATCH v2 0/9] Harden list_for_each_entry_rcu() and family Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 1/9] rcu/update: Remove useless check for debug_locks Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 2/9] rcu: Add support for consolidated-RCU reader checking Joel Fernandes (Google)
2019-07-16 18:22 ` Paul E. McKenney
2019-07-16 18:35 ` Joel Fernandes
2019-07-16 18:50 ` Paul E. McKenney
2019-07-12 17:00 ` [PATCH v2 3/9] rcu/sync: Remove custom check for reader-section Joel Fernandes (Google)
2019-07-12 21:35 ` Joel Fernandes [this message]
2019-07-12 23:32 ` Paul E. McKenney
2019-07-13 3:01 ` Joel Fernandes
2019-07-13 3:10 ` Joel Fernandes
2019-07-13 8:21 ` Paul E. McKenney
2019-07-13 13:30 ` Joel Fernandes
2019-07-13 14:41 ` Paul E. McKenney
2019-07-13 15:36 ` Joel Fernandes
2019-07-13 15:50 ` Paul E. McKenney
2019-07-13 16:13 ` Joel Fernandes
2019-07-13 21:28 ` Paul E. McKenney
2019-07-14 18:10 ` Joel Fernandes
2019-07-14 18:38 ` Joel Fernandes
2019-07-14 18:50 ` Paul E. McKenney
2019-07-15 7:26 ` Oleg Nesterov
2019-07-16 18:26 ` Paul E. McKenney
2019-07-16 18:28 ` Paul E. McKenney
2019-07-12 17:00 ` [PATCH v2 4/9] ipv4: add lockdep condition to fix for_each_entry Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 5/9] driver/core: Convert to use built-in RCU list checking Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 6/9] workqueue: Convert for_each_wq to use built-in list check Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 7/9] x86/pci: Pass lockdep condition to pcm_mmcfg_list iterator Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 8/9] acpi: Use built-in RCU list checking for acpi_ioremaps list Joel Fernandes (Google)
2019-07-12 17:00 ` [PATCH v2 9/9] doc: Update documentation about list_for_each_entry_rcu Joel Fernandes (Google)
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