From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Byungchul Park <byungchul.park@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Peter Hurley <peter@hurleysoftware.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
akpm@linux-foundation.org, mingo@kernel.org,
linux-kernel@vger.kernel.org, akinobu.mita@gmail.com,
jack@suse.cz, torvalds@linux-foundation.org
Subject: Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code
Date: Fri, 29 Jan 2016 16:13:30 +0900 [thread overview]
Message-ID: <20160129071330.GH4820@swordfish> (raw)
In-Reply-To: <20160129065407.GE31266@X58A-UD3R>
On (01/29/16 15:54), Byungchul Park wrote:
> On Fri, Jan 29, 2016 at 09:27:03AM +0900, Sergey Senozhatsky wrote:
> >
> > well, the stack is surely limited, but on every
> > spin_dump()->spin_lock() recursive call it does another
> > round of
> >
> > u64 loops = loops_per_jiffy * HZ;
> >
> > for (i = 0; i < loops; i++) {
> > if (arch_spin_trylock(&lock->raw_lock))
> > return;
> > __delay(1);
> > }
> >
> > so if you have 1000 spin_dump()->spin_lock() then, well,
> > something has been holding the lock for '1000 * loops_per_jiffy * HZ'.
>
> Or the printk() is heavily called and the lock is congested.
well, isn't it the case that ticket-based locking assumes at least
some sort of fairness? how many cpus do you have there? you can
have `num_online_cpus() - 1' tasks spinning on the spin lock and
1 owning the spin lock... if your lock is in correct state (no
before/after spinlock debug errors) even most unlucky task should
get the lock eventually...
-ss
next prev parent reply other threads:[~2016-01-29 7:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-27 12:01 [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park
2016-01-27 22:49 ` Peter Hurley
2016-01-28 7:15 ` Byungchul Park
2016-01-29 8:19 ` Byungchul Park
2016-01-28 1:42 ` Byungchul Park
2016-01-28 2:37 ` Sergey Senozhatsky
2016-01-28 4:36 ` byungchul.park
2016-01-28 6:05 ` Sergey Senozhatsky
2016-01-28 8:13 ` Byungchul Park
2016-01-28 10:41 ` Sergey Senozhatsky
2016-01-28 10:53 ` Sergey Senozhatsky
2016-01-28 15:42 ` Sergey Senozhatsky
2016-01-28 23:08 ` Peter Hurley
2016-01-28 23:54 ` Byungchul Park
2016-01-29 0:54 ` Sergey Senozhatsky
2016-01-29 3:00 ` Byungchul Park
2016-01-29 4:05 ` Sergey Senozhatsky
2016-01-29 12:15 ` Byungchul Park
2016-01-29 0:27 ` Sergey Senozhatsky
2016-01-29 4:32 ` Peter Hurley
2016-01-29 5:28 ` Sergey Senozhatsky
2016-01-29 5:48 ` Peter Hurley
2016-01-29 6:16 ` Sergey Senozhatsky
2016-01-29 6:37 ` Sergey Senozhatsky
2016-01-31 12:30 ` Sergey Senozhatsky
2016-01-31 12:33 ` [PATCH 1/3] printk: introduce console_reset_on_panic() function Sergey Senozhatsky
2016-01-31 12:33 ` [PATCH 2/3] printk: introduce reset_console_drivers() Sergey Senozhatsky
2016-01-31 12:47 ` kbuild test robot
2016-01-31 12:33 ` [PATCH 3/3] spinlock_debug: panic on recursive lock spin_dump() Sergey Senozhatsky
2016-02-01 16:14 ` Sergey Senozhatsky
2016-02-02 7:59 ` Sergey Senozhatsky
2016-01-31 12:42 ` [PATCH 1/3] printk: introduce console_reset_on_panic() function kbuild test robot
2016-01-29 6:54 ` [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in the debug code Byungchul Park
2016-01-29 7:13 ` Sergey Senozhatsky [this message]
2016-01-29 8:13 ` Byungchul Park
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