From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.codeaurora.org ([198.145.11.231]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1XxWOs-0007Gg-PV for linux-mtd@lists.infradead.org; Sun, 07 Dec 2014 07:37:03 +0000 Message-ID: <54840385.5040305@codeaurora.org> Date: Sun, 07 Dec 2014 09:36:37 +0200 From: Tanya Brokhman MIME-Version: 1.0 To: Richard Weinberger , dedekind1@gmail.com Subject: Re: [PATCH 4/6] UBI: Fastmap: Fix races in ubi_wl_get_peb() References: <1416835236-25185-1-git-send-email-richard@nod.at> <1416835236-25185-5-git-send-email-richard@nod.at> <5481AE79.1090900@codeaurora.org> <5481B120.5020409@nod.at> <5481E336.8090303@codeaurora.org> <54821EC3.3030107@nod.at> In-Reply-To: <54821EC3.3030107@nod.at> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 12/5/2014 11:08 PM, Richard Weinberger wrote: > >>>>> spin_unlock(&ubi->wl_lock); >>>>> + if (retried) { >>>>> + ubi_err(ubi, "Unable to get a free PEB from user WL pool"); >>>>> + ret = -ENOSPC; >>>>> + goto out; >>>>> + } >>>>> + retried = 1; >>>> >>>> Why did you decide to retry in this function? and why only 1 retry attempt? I'm not against it, trying to understand the logic. >>> >>> Because failing immediately with -ENOSPC is not nice. >> >> Why not? this is what was done before.... > > The behavior from before was not good. > If we return here a -ENOSPC it is not because we ran out of free PEBs, it is because the pool contains > no free PEBs and needs refilling. > As between refilling the pool and requesting a fresh PEB from it another thread could "steal" all PEBs > we retry. > >> I think what I really bothers me in this case is that you don't sleep, you branch immediately to retry again, so the chances that there will be context switch and free pebs appear >> aren't that high. >> I'm used to functions using some sort of "retry" logic to sleep before retrying. Of course sleeping isn't a good idea here. That's why the "retry" bugs me a bit. > > You mean a cond_resched()? > This retry-logic is common pattern in UBI. For exmaple see ubi_wl_put_peb(). you're right. didn't pay much attention to ubi_wl_put_peb() before. don't like it there either :) perhaps we can rethink this later for both cases. > > Thanks, > //richard > Thanks, Tanya Brokhman -- Qualcomm Israel, on behalf of Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project