From: Alex Zeffertt <ajz@cambridgebroadband•com>
To: Scott Wood <scottwood@freescale•com>
Cc: linuxppc-embedded@ozlabs•org
Subject: Re: local_irq_save not masking interrupts
Date: Tue, 26 Sep 2006 17:42:42 +0100 [thread overview]
Message-ID: <45195882.1090003@cambridgebroadband.com> (raw)
In-Reply-To: <451954D8.3050909@freescale.com>
Scott Wood wrote:
> Alex Zeffertt wrote:
>> I agree this indicates an intent to make it atomic, but I don't see how
>> this could cause interrupts to become re-enabled during the request_irq()
>> call. Also, since I am calling request_irq at insmod time, i.e. in
>> process
>> context, both GFP_ flags *should* work.
>
> You're effectively not in process context when you disable IRQs (at
> least, if you want them to stay that way). By specifying GFP_KERNEL,
> you're giving the allocator permission to go to sleep, enable IRQs, etc.
> The IRQ enabling will happen any time cache_grow() is called with
> GFP_WAIT (which is part of GFP_KERNEL), assuming a growable slab.
Ah-ha! This explains a lot...
One of the oddities I was seeing with this problem was that if I
did an "ifconfig down" on a completely unrelated net_device (a vlan)
the problem would *not* occur, i.e. I did not get an interrupt
during the critical section. Now I understand why: the "ifconfig down"
command freed some memory so that the kmalloc(,GFP_KERNEL) did not
need to grow the cache.
It follows from what you are saying that kmalloc(,GFP_KERNEL)
MUST NOT occur anywhere in the call chain during a critical section.
This must catch others out too. Surely kmalloc/cache_grow should
return NULL rather than enable interrupts. In fact, shouldn't it be
a BUG() if kmalloc(,GFP_KERNEL) is called with IRQs disabled?
Thanks for your explanation!
Alex
next prev parent reply other threads:[~2006-09-26 16:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-26 10:00 local_irq_save not masking interrupts Alex Zeffertt
2006-09-26 10:19 ` Liu Dave-r63238
2006-09-26 10:28 ` Alex Zeffertt
2006-09-26 16:02 ` Scott Wood
2006-09-26 16:17 ` Alex Zeffertt
2006-09-26 16:27 ` Scott Wood
2006-09-26 16:42 ` Alex Zeffertt [this message]
2006-09-26 16:52 ` Scott Wood
2006-09-27 16:52 ` Esben Nielsen
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