linux-kernel - Re: [PATCH] Allow __vmalloc with GFP

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Message-ID: <20070428075240.GA8256@flint.arm.linux.org.uk>
Date:	Sat, 28 Apr 2007 08:52:41 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Giridhar Pemmasani <pgiri@...oo.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Allow __vmalloc with GFP_ATOMIC

On Fri, Apr 27, 2007 at 09:03:33PM -0700, Giridhar Pemmasani wrote:
> Until 2.6.19, __vmalloc with GFP_ATOMIC was possible, but __get_vm_area_node
> would allocate the node itself with GFP_KERNEL, causing a warning. In 2.6.19,
> this was "fixed" by using the same flags that were passed to __vmalloc also
> in __get_vm_area_node. However, __get_vm_area_node does
> BUG_ON(in_interrupt()) now, since vmlist_lock is obtained without disabling
> bottom-half's. The patch below uses bh disabled lock for vmlist_lock, so that
> __vmalloc can be used in interrupt context.

It's worse than that.  If vmalloc has to allocate a page table, the
allocation will be done as a non-atomic allocation.  So, even if you
do fix __get_vm_area_node and all the other cases, if you hit a page
table allocation you'll still get a warning.

Folk need to accept that using vmalloc from atomic contexts is a
complete nono.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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