linux-kernel - Re: can a kmalloc be both GFP_ATOMIC and GFP

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Message-ID: <20070428152040.GA3558@localhost.localdomain>
Date:	Sat, 28 Apr 2007 23:20:40 +0800
From:	WANG Cong <xiyou.wangcong@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Robert P. J. Day" <rpjday@...dspring.com>,
	"Shan, Guo Wen (Gavin)" <gshan@...atel-lucent.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: can a kmalloc be both GFP_ATOMIC and GFP_KERNEL at the same time?

On Sat, Apr 28, 2007 at 08:03:42AM -0700, Arjan van de Ven wrote:
>
>> >
>> >
>> >   i'd always assumed that the type flags of GFP_ATOMIC and GFP_KERNEL
>> > were mutually exclusive when it came to calling kmalloc(), at least
>> > based on everything i'd read.  so i'm not sure how to interpret the
>> > following:
>> >
>> > drivers/scsi/aic7xxx_old.c:  aic_dev = kmalloc(sizeof(struct aic_dev_data), GFP_ATOMIC | GFP_KERNEL);
>> > drivers/message/i2o/device.c:   resblk = kmalloc(buflen + 8, GFP_KERNEL | GFP_ATOMIC);
>> >
>> >   clarification?
>> 
>> oh, i'm *aware* of the definitions of those flags, but every single
>> source i've ever read has *strongly* suggested that you don't use
>> those two flags together so i was surprised to see those combinations.
>> (as an example, love's kernel book, p. 192, shows a table of valid
>> combinations of flags to use, but doesn't mention the one above.)
>> 
>> and, on the other hand, if they *are* legal to use together, i guess
>> i'm kind of surprised that there would be only two instances of it.
>
>it's not legal to use the combo; you have found yourself a very genuine
>bug here! Good spotting!

Yes. LDD already talked about this. GFP_KERNEL may cause sleeping while GFP_ATOMIC not. Combining them is confusing. 


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