Re: [PATCH] ata: fix sleep-while-holding-spinlock in sata_nv

From: Robert Hancock
Date: Wed May 21 2008 - 10:33:47 EST

rjan van de Ven wrote:
I'm not certain this is safe to do it quite this way. It would be
better to keep that spinlock held so that no operations could be in
progress on either port while these operations are happening.

blk_bounce_limit can sleep. that's just a fact of life ;(

Now it can, for no reason. Under the conditions it was used before, it never could.

It would be better to fix the regression from 419c434c35614609fd0c79d335c134bf4b88b30b in block/blk_settings.c that resulted in the blk_queue_bounce_limit allocation wrongly allocating emergency ISA pages in the first place as a 32-bit DMA mask does not need them.

the condition under which it sleeps might be slightly buggy on your
exact x86 machine... but that doesn't mean that that is guaranteed to
be so forever going forward.... it's still a sleeping function.

More than slightly buggy, I think.. It seems like it is going to be bouncing block layer accesses to devices with 32-bit DMA masks through the 16MB ZONE_DMA. If that's what's actually going on, I'm surprised there haven't been more regression reports. The fact that the function now sleeps when it didn't before is the least of the problems here..
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