linux-kernel - RE: efi_pstore: question about how to remove create_sysfs

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Date:	Tue, 14 Aug 2012 19:29:26 +0000
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Mike Waychison <mikew@...gle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Luck, Tony (tony.luck@...el.com)" <tony.luck@...el.com>,
	"Matthew Garrett (mjg@...hat.com)" <mjg@...hat.com>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: efi_pstore: question about how to remove create_sysfs_entry()
 from a write callback.

Mike,

Previous pseudo code was not correct.
More precisely, it is as follows.
But, we still need to alloc memory dynamically in the part of <Save information about new entry>
because a workqueue can't know how many new entries in advance.

 spin_lock_irqsave(&efivars_lock);
 
 do {
 	get_next_variable();
 	if (found new entry)
  		<Save information about new entry>
 
 } while()
 
 spin_lock_irqrestore(&efivars_lock);

  efivars_create_sysfs_entries();

Seiji

> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Seiji Aguchi
> Sent: Tuesday, August 14, 2012 2:52 PM
> To: Mike Waychison
> Cc: linux-kernel@...r.kernel.org; Luck, Tony (tony.luck@...el.com); Matthew Garrett (mjg@...hat.com); dzickus@...hat.com; dle-
> develop@...ts.sourceforge.net; Satoru Moriya
> Subject: RE: efi_pstore: question about how to remove create_sysfs_entry() from a write callback.
> 
> > Can we not serialize this with &efivars->lock if it is updated to
> > disable interrupts?  A loop in the workqueue that locks, iterates
> > through
> > ->get_next_variable, and compares against searches in
> > efivars->list should work, no?
> 
> If my understanding is correct, your pseudo code is as follows.
> 
> spin_lock_irqsave(&efivars_lock);
> 
> do {
> 	get_next_variable();
> 	if (found new entry)
>  		efivars_create_sysfs_entries();
> 
> } while()
> 
> spin_lock_irqrestore(&efivars_lock);
> 
> But, memory is allocated dynamically with kzalloc() in efivars_create_sysfs_entries().
> I don't want to allocate memory  while holding spin_lock.
> 
> Please let me know if I'm missing something.
> 
> Seiji
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