On Thu, 2018-07-26 at 08:25 +0200, Richard Weinberger wrote: > Ben, > > Am Donnerstag, 26. Juli 2018, 04:12:54 CEST schrieb Ben Hutchings: > > On Tue, 2018-07-10 at 20:24 +0200, Greg Kroah-Hartman wrote: > > > 4.4-stable review patch. If anyone has any objections, please let me know. > > > > > > ------------------ > > > > > > From: Richard Weinberger <richard@xxxxxx> > > > > > > commit 781932375ffc6411713ee0926ccae8596ed0261c upstream. > > > > > > Fastmap cannot track the LEB unmap operation, therefore it can > > > happen that after an interrupted erasure the mapping still looks > > > good from Fastmap's point of view, while reading from the PEB will > > > cause an ECC error and confuses the upper layer. > > > > > > Instead of teaching users of UBI how to deal with that, we read back > > > the VID header and check for errors. If the PEB is empty or shows ECC > > > errors we fixup the mapping and schedule the PEB for erasure. > > > > [...] > > > > Isn't there a risk here, that a read error leads to erasing data that > > might be recoverable if the read is retried? > > Well, read error means that already something went very wrong. At other places > in UBI wo also don't retry reading headers and consider it as fatal when we > are unable to read it. > We could also read the EC header, but what do we gain from that? > If the VID header is not readable we cannot check fastmap either. > > What case exactly do you have in mind? I suppose I'm thinking about data recovery from a flash device that has become unreliable. I'm not familiar with ubi; is there a read-only mode where the erase wouldn't actually be performed? Ben. -- Ben Hutchings, Software Developer Codethink Ltd https://www.codethink.co.uk/ Dale House, 35 Dale Street Manchester, M1 2HF, United Kingdom
