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Message-ID: <20160129065407.GE31266@X58A-UD3R>
Date: Fri, 29 Jan 2016 15:54:07 +0900
From: Byungchul Park <byungchul.park@....com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Peter Hurley <peter@...leysoftware.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
akpm@...ux-foundation.org, mingo@...nel.org,
linux-kernel@...r.kernel.org, akinobu.mita@...il.com, jack@...e.cz,
torvalds@...ux-foundation.org
Subject: Re: [PATCH v4] lib/spinlock_debug.c: prevent a recursive cycle in
the debug code
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.
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