Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: Q: semaphore and kmalloc(GFP_KERNEL)? | Date | Mon, 11 May 2009 11:56:02 +0900 (JST) |
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> Hello. > I got a question. > > When we use kmalloc(GFP_KERNEL), we cannot use spinlock. > We use semaphore instead. > > What happens if a writer process got into sleep state at kmalloc() > without releasing a rw_semaphore for writing, > > down_write(&sem); > list_for_each() > ...; > ptr = kmalloc(size, GFP_KERNEL); > list_add(); > up_write(&sem); > > and then reader processes tried to hold that rw_semaphore? > > down_read(&sem); > list_for_each() > ...; > up_read(&sem); > > Can the kernel detect that we need to let kmalloc() fail and > wake up the writer process so that the writer process releases > the rw_semaphore and reader processes can continue?
it can't. Plus it shouldn't. some caller don't want kmalloc() failure.
> (If the kernel can't detect, I worry that we experience > all processes sleeping for undefined duration.)
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