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Date: Mon, 26 Apr 2010 16:32:53 +0200 From: Jörn Engel <joern@...fs.org> To: Jens Axboe <jens.axboe@...cle.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, David Woodhouse <dwmw2@...radead.org>, linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org, Christoph Hellwig <hch@...radead.org>, Paolo Minazzi <paolo.minazzi@...il.com> Subject: Re: [Patch] Catch filesystems lacking s_bdi On Mon, 26 April 2010 11:48:11 +0200, Jens Axboe wrote: > On Fri, Apr 23 2010, Jörn Engel wrote: > > On Fri, 23 April 2010 12:05:32 +0200, Jens Axboe wrote: > > > > > > So it's probably safe and good enough as-is, I'll add it. Thanks! > > > > I cannot see this patch in your tree yet. Could be the weekend or a > > deliberate decision not to send this for 2.6.34-rc anymore. > > It's there, I put it in yesterday. It's definitely 2.6.34-rc material, I > hope to submit it tonight. Ok, thanks. > > In case it was a deliberate decision, can we please make it explicit? I > > don't like the idea of adding a BUG_ON() that potentially triggers for > > thousands of people this late in the stabilization process - but it is > > better than having people lose data. Even if we already ran two stable > > kernels that way. > > > > Damned if you do, damned if you don't. :( > > Yeah, it's a bad situation to be in. I changed that BUG_ON() to a > WARN_ON(). I'm not too worried about that part, I'm more worried about > the file system changed. OTOH, they do lack proper flushing now, so it's > likely not a huge risk from that perspective. It is worse still. Using mtd->backing_dev_info results in kernel BUG at fs/fs-writeback.c:157 which is BUG_ON(!work->seen); in bdi_queue_work(). Logfs is affected and I bet jffs2 is as well. So much for dwmw2 or me actually testing the fix. :( I did a hexdump to see what sb->s_bdi actually contained and the result was this: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 ........ Which should be mtd_bdi_unmappable. And at this point I have to admit being clueless. What exactly should a struct backing_dev_info contain and for what purposes? And where is this documented? Jörn -- He who knows others is wise. He who knows himself is enlightened. -- Lao Tsu -- 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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