From: Julien Grall <julien@xen.org>
To: Roger Pau Monne <roger.pau@citrix.com>, xen-devel@lists.xenproject.org
Cc: Igor Druzhinin <igor.druzhinin@citrix.com>,
Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Jan Beulich <jbeulich@suse.com>
Subject: Re: [PATCH] xen/spinlock: move debug helpers inside the locked regions
Date: Wed, 29 Jul 2020 14:37:44 +0100 [thread overview]
Message-ID: <16dd0f04-598b-8b84-8a25-6b89af9214d7@xen.org> (raw)
In-Reply-To: <20200729111330.64549-1-roger.pau@citrix.com>
Hi Roger,
On 29/07/2020 12:13, Roger Pau Monne wrote:
> Debug helpers such as lock profiling or the invariant pCPU assertions
> must strictly be performed inside the exclusive locked region, or else
> races might happen.
>
> Note the issue was not strictly introduced by the pointed commit in
> the Fixes tag, since lock stats where already incremented before the
> barrier, but that commit made it more apparent as manipulating the cpu
> field could happen outside of the locked regions and thus trigger the
> BUG_ON.
From the wording, it is not entirely clear which BUG_ON() you are
referring to. I am guessing, it is the one in rel_lock(). Am I correct?
Otherwise, the change looks good to me.
Cheers,
> This is only enabled on debug builds, and thus releases are
> not affected.
>
> Fixes: 80cba391a35 ('spinlocks: in debug builds store cpu holding the lock')
> Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> ---
> xen/common/spinlock.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
> index 17f4519fc7..ce3106e2d3 100644
> --- a/xen/common/spinlock.c
> +++ b/xen/common/spinlock.c
> @@ -170,9 +170,9 @@ void inline _spin_lock_cb(spinlock_t *lock, void (*cb)(void *), void *data)
> cb(data);
> arch_lock_relax();
> }
> + arch_lock_acquire_barrier();
> got_lock(&lock->debug);
> LOCK_PROFILE_GOT;
> - arch_lock_acquire_barrier();
> }
>
> void _spin_lock(spinlock_t *lock)
> @@ -198,9 +198,9 @@ unsigned long _spin_lock_irqsave(spinlock_t *lock)
>
> void _spin_unlock(spinlock_t *lock)
> {
> - arch_lock_release_barrier();
> LOCK_PROFILE_REL;
> rel_lock(&lock->debug);
> + arch_lock_release_barrier();
> add_sized(&lock->tickets.head, 1);
> arch_lock_signal();
> preempt_enable();
> @@ -249,15 +249,15 @@ int _spin_trylock(spinlock_t *lock)
> preempt_enable();
> return 0;
> }
> + /*
> + * cmpxchg() is a full barrier so no need for an
> + * arch_lock_acquire_barrier().
> + */
> got_lock(&lock->debug);
> #ifdef CONFIG_DEBUG_LOCK_PROFILE
> if (lock->profile)
> lock->profile->time_locked = NOW();
> #endif
> - /*
> - * cmpxchg() is a full barrier so no need for an
> - * arch_lock_acquire_barrier().
> - */
> return 1;
> }
>
>
--
Julien Grall
next prev parent reply other threads:[~2020-07-29 13:38 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-29 11:13 [PATCH] xen/spinlock: move debug helpers inside the locked regions Roger Pau Monne
2020-07-29 13:37 ` Julien Grall [this message]
2020-07-29 13:50 ` Roger Pau Monné
2020-07-29 14:57 ` Julien Grall
2020-07-30 18:29 ` Julien Grall
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