From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from a.ns.miles-group.at ([95.130.255.143] helo=radon.swed.at) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1XxYPP-00080c-LZ for linux-mtd@lists.infradead.org; Sun, 07 Dec 2014 09:45:45 +0000 Message-ID: <548421AB.90303@nod.at> Date: Sun, 07 Dec 2014 10:45:15 +0100 From: Richard Weinberger MIME-Version: 1.0 To: Tanya Brokhman , 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> <54840385.5040305@codeaurora.org> In-Reply-To: <54840385.5040305@codeaurora.org> Content-Type: text/plain; charset=windows-1252 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: , Am 07.12.2014 um 08:36 schrieb Tanya Brokhman: > 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. If there is room for improvement I'm all open for an extra patch set all over UBI. :-) Thanks, //richard