Messages in this thread | | | Subject | Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in decompression | From | Chao Yu <> | Date | Wed, 9 Dec 2020 09:34:06 +0800 |
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On 2020/12/9 7:55, Jaegeuk Kim wrote: > On 12/07, Eric Biggers wrote: >> On Tue, Dec 08, 2020 at 08:51:45AM +0900, Daeho Jeong wrote: >>>> I am trying to review this but it is very hard, as the f2fs compression code is >>>> very hard to understand. >>>> >>>> It looks like a 'struct decompress_io_ctx' represents the work to decompress a >>>> particular cluster. Since the compressed data of the cluster can be read using >>>> multiple bios, there is a reference count of how many pages are remaining to be >>>> read before all the cluster's pages have been read and decompression can start. >>>> >>>> What I don't understand is why that reference counting needs to work differently >>>> depending on whether verity is enabled or not. Shouldn't it be exactly the >>>> same? >>>> >>>> There also seems to be some confusion about the scope of STEP_VERITY. Before >>>> f2fs compression was added, it was a per-bio thing. But now in a compressed >>>> file, it's really a per-cluster thing, since all decompressed pages in a >>>> compressed cluster are verified (or not verified) at once. >>>> >>>> Wouldn't it make a lot more sense to, when a cluster needs both compression and >>>> verity, *not* set STEP_VERITY on the bios, but rather set a similar flag in the >>>> decompress_io_ctx? >>>> >>> >>> Eric, >>> >>> Decompression and verity can be executed in different thread contexts >>> in different timing, so we need separate counts for each. >>> >>> We already use STEP_VERITY for non-compression case, so I think using >>> this flag in here looks more making sense. >>> >>> Thanks, >> >> That didn't really answer my questions. >> >> I gave up trying to review this patch as the compression post-read handling is >> just way too weird and hard to understand. I wrote a patch to clean it all up >> instead, please take a look: >> https://lkml.kernel.org/r/20201208060328.2237091-1-ebiggers@kernel.org > > Eric, > I also tried to review your patch, but it's quite hard to follow quickly and
Me too, it needs more time to check whether the cleanup doesn't miss any cases.
Thanks,
> requires stress tests for a while. Given upcoming merge window and urgency of > the bug, let me apply Daeho's fix first. By any chance, may I ask revisiting > your clean-up on top of the fix in the next cycle? > > Thanks, > >> >> - Eric > > > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > . >
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