linux-kernel - Re: [RFC PATCH] Introduce filesystem type tracking

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Message-ID: <7b9198260805200836q6b9ad5f0x3b42c8f6c933fa21@mail.gmail.com>
Date:	Tue, 20 May 2008 16:36:50 +0100
From:	"Tom Spink" <tspink@...il.com>
To:	"Matthew Wilcox" <matthew@....cx>
Cc:	"Christoph Hellwig" <hch@...radead.org>,
	"Al Viro" <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH] Introduce filesystem type tracking

2008/5/20 Matthew Wilcox <matthew@....cx>:
> On Tue, May 20, 2008 at 04:18:14PM +0100, Tom Spink wrote:
>> +
>> +     mutex_lock(&type->fs_supers_lock);
>> +     if (list_empty(&type->fs_supers) && type->init) {
>> +             err = type->init();
>> +             if (err) {
>> +                     mutex_unlock(&type->fs_supers_lock);
>> +                     spin_unlock(&sb_lock);
>> +                     destroy_super(s);
>> +                     return ERR_PTR(err);
>> +             }
>> +     }
>> +
>> +     list_add(&s->s_instances, &type->fs_supers);
>> +     mutex_unlock(&type->fs_supers_lock);
>> +
>>       s->s_type = type;
>>       strlcpy(s->s_id, type->name, sizeof(s->s_id));
>>       list_add_tail(&s->s_list, &super_blocks);
>> -     list_add(&s->s_instances, &type->fs_supers);
>> +
>>       spin_unlock(&sb_lock);
>
> You can't take a mutex while holding a spinlock -- what if you had to
> sleep to acquire the mutex?
>
> I imagine you also don't want to hold a spinlock while calling the
> ->init or ->exit -- what if the fs wants to sleep in there (eg allocate
> memory with GFP_KERNEL).
>
> --
> Intel are signing my paycheques ... these opinions are still mine
> "Bill, look, we understand that you're interested in selling us this
> operating system, but compare it to ours.  We can't possibly take such
> a retrograde step."
>

Oh no!  This is bad.  I really need to devise some script to stress
test my code - and also make myself pay attention to what I'm doing.
Sorry for the noise, guys.

-- 
Tom Spink
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