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Message-ID: <20150211033720.GA20820@mew> Date: Tue, 10 Feb 2015 19:37:20 -0800 From: Omar Sandoval <osandov@...ndov.com> To: Chris J Arges <chris.j.arges@...onical.com> Cc: Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, Lukáš Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4] ext4: fix indirect punch hole corruption On Tue, Feb 10, 2015 at 08:59:23PM -0600, Chris J Arges wrote: > On 02/10/2015 03:44 PM, Omar Sandoval wrote: > > Commit 4f579ae7de56 (ext4: fix punch hole on files with indirect > > mapping) rewrote FALLOC_FL_PUNCH_HOLE for ext4 files with indirect > > mapping. However, there are bugs in several corner cases. This fixes 5 > > distinct bugs: > > > > 1. When there is at least one entire level of indirection between the > > start and end of the punch range and the end of the punch range is the > > first block of its level, we can't return early; we have to free the > > intervening levels. > > > > 2. When the end is at a higher level of indirection than the start and > > ext4_find_shared returns a top branch for the end, we still need to free > > the rest of the shared branch it returns; we can't decrement partial2. > > > > 3. When a punch happens within one level of indirection, we need to > > converge on an indirect block that contains the start and end. However, > > because the branches returned from ext4_find_shared do not necessarily > > start at the same level (e.g., the partial2 chain will be shallower if > > the last block occurs at the beginning of an indirect group), the walk > > of the two chains can end up "missing" each other and freeing a bunch of > > extra blocks in the process. This mismatch can be handled by first > > making sure that the chains are at the same level, then walking them > > together until they converge. > > > > 4. When the punch happens within one level of indirection and > > ext4_find_shared returns a top branch for the start, we must free it, > > but only if the end does not occur within that branch. > > > > 5. When the punch happens within one level of indirection and > > ext4_find_shared returns a top branch for the end, then we shouldn't > > free the block referenced by the end of the returned chain (this mirrors > > the different levels case). > > > > Signed-off-by: Omar Sandoval <osandov@...ndov.com> > > --- > > Okay, two more bugfixes folded in, all described in the commit message. > > I'm finally no longer seeing xfstest generic/270 cause corruptions, even > > after running it overnight, so hopefully this is it. Chris, would you > > mind trying this out? > > > > Omar, > I've completed 80 iterations of this patch so far without failure! > Normally failures have occurred between 2-15 runs. Great job, and thanks > for your persistence in fixing this issue! > > Tested-by: Chris J Arges <chris.j.arges@...onical.com> > Awesome, I was starting to run out of ideas ;) Thanks for all of your testing. Lukáš, would you like to take a look at this? Also, Ted and Andreas, would you prefer this all in one patch, or should I split out each individual fix into its own patch? Thanks! -- Omar -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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