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Date: Mon, 11 May 2009 11:56:02 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> Cc: kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org Subject: Re: Q: semaphore and kmalloc(GFP_KERNEL)? > 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.) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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