From: Eric Biggers <ebiggers@kernel.org>
To: linux-f2fs-devel@lists.sourceforge.net,
Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Fri, 30 Jul 2021 12:17:26 -0700 [thread overview]
Message-ID: <YQRQRh1zUHSIzcC/@gmail.com> (raw)
In-Reply-To: <20210728015154.171507-1-ebiggers@kernel.org>
On Tue, Jul 27, 2021 at 06:51:54PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> Currently, non-overwrite DIO writes are fundamentally unsafe on f2fs as
> they require preallocating blocks, but f2fs doesn't support unwritten
> blocks and therefore has to preallocate the blocks as regular blocks.
> f2fs has no way to reliably roll back such preallocations, so as a
> result, f2fs will leak uninitialized blocks to users if a DIO write
> doesn't fully complete. This can be easily reproduced by issuing a DIO
> write that will fail due to misalignment, e.g.:
>
> rm -f file
> truncate -s 1000000 file
> dd if=/dev/zero bs=999999 oflag=direct conv=notrunc of=file
> od -tx1 file # shows uninitialized disk blocks
>
> Until a proper design for non-overwrite DIO writes on f2fs can be
> designed and implemented, remove support for them and make them fall
> back to buffered I/O. This is what other filesystems that don't support
> unwritten blocks, e.g. ext2, also do, at least for non-extending DIO
> writes. However, f2fs can't do extending DIO writes either, as f2fs
> appears to have no mechanism for guaranteeing that leftover allocated
> blocks past EOF will get truncated. (f2fs does have an orphan list, but
> it's only used for deleting inodes, not truncating them.)
>
> This patch doesn't attempt to remove the F2FS_GET_BLOCK_{DIO,PRE_DIO}
> cases in f2fs_map_blocks(); that can be cleaned up later.
>
> Fixes: bfad7c2d4033 ("f2fs: introduce a new direct_IO write path")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
Any opinion on this patch? This really needs to be fixed one way or another.
Probably before the conversion to iomap, as this fix will need to be backported.
- Eric
WARNING: multiple messages have this Message-ID (diff)
From: Eric Biggers <ebiggers@kernel.org>
To: linux-f2fs-devel@lists.sourceforge.net,
Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes
Date: Fri, 30 Jul 2021 12:17:26 -0700 [thread overview]
Message-ID: <YQRQRh1zUHSIzcC/@gmail.com> (raw)
In-Reply-To: <20210728015154.171507-1-ebiggers@kernel.org>
On Tue, Jul 27, 2021 at 06:51:54PM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> Currently, non-overwrite DIO writes are fundamentally unsafe on f2fs as
> they require preallocating blocks, but f2fs doesn't support unwritten
> blocks and therefore has to preallocate the blocks as regular blocks.
> f2fs has no way to reliably roll back such preallocations, so as a
> result, f2fs will leak uninitialized blocks to users if a DIO write
> doesn't fully complete. This can be easily reproduced by issuing a DIO
> write that will fail due to misalignment, e.g.:
>
> rm -f file
> truncate -s 1000000 file
> dd if=/dev/zero bs=999999 oflag=direct conv=notrunc of=file
> od -tx1 file # shows uninitialized disk blocks
>
> Until a proper design for non-overwrite DIO writes on f2fs can be
> designed and implemented, remove support for them and make them fall
> back to buffered I/O. This is what other filesystems that don't support
> unwritten blocks, e.g. ext2, also do, at least for non-extending DIO
> writes. However, f2fs can't do extending DIO writes either, as f2fs
> appears to have no mechanism for guaranteeing that leftover allocated
> blocks past EOF will get truncated. (f2fs does have an orphan list, but
> it's only used for deleting inodes, not truncating them.)
>
> This patch doesn't attempt to remove the F2FS_GET_BLOCK_{DIO,PRE_DIO}
> cases in f2fs_map_blocks(); that can be cleaned up later.
>
> Fixes: bfad7c2d4033 ("f2fs: introduce a new direct_IO write path")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
Any opinion on this patch? This really needs to be fixed one way or another.
Probably before the conversion to iomap, as this fix will need to be backported.
- Eric
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next prev parent reply other threads:[~2021-07-30 19:17 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-28 1:51 [f2fs-dev] [PATCH] f2fs: remove broken support for allocating DIO writes Eric Biggers
2021-07-28 1:51 ` Eric Biggers
2021-07-30 19:17 ` Eric Biggers [this message]
2021-07-30 19:17 ` Eric Biggers
2021-07-30 22:12 ` [f2fs-dev] " Jaegeuk Kim
2021-07-30 22:12 ` Jaegeuk Kim
2021-07-30 22:19 ` Eric Biggers
2021-07-30 22:19 ` [f2fs-dev] " Eric Biggers
2021-07-31 1:05 ` Jaegeuk Kim
2021-07-31 1:05 ` [f2fs-dev] " Jaegeuk Kim
2021-07-31 1:18 ` Eric Biggers
2021-07-31 1:18 ` Eric Biggers
2021-07-31 2:46 ` Theodore Ts'o
2021-07-31 2:46 ` [f2fs-dev] " Theodore Ts'o
2021-08-02 4:39 ` Eric Biggers
2021-08-02 4:39 ` Eric Biggers
2021-08-02 9:00 ` Chao Yu
2021-08-02 9:00 ` [f2fs-dev] " Chao Yu
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-02 18:23 ` Jaegeuk Kim
2021-08-03 1:19 ` [f2fs-dev] " Chao Yu
2021-08-03 1:19 ` Chao Yu
2021-08-03 1:34 ` [f2fs-dev] " Jaegeuk Kim
2021-08-03 1:34 ` Jaegeuk Kim
2021-08-17 2:03 ` [f2fs-dev] " Eric Biggers
2021-08-17 2:03 ` Eric Biggers
2021-08-17 5:42 ` [f2fs-dev] " Christoph Hellwig
2021-08-17 5:42 ` Christoph Hellwig
2021-08-17 18:57 ` Jaegeuk Kim
2021-08-17 18:57 ` [f2fs-dev] " Jaegeuk Kim
2021-08-17 20:27 ` Eric Biggers
2021-08-17 20:27 ` [f2fs-dev] " Eric Biggers
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-17 21:33 ` Jaegeuk Kim
2021-08-18 0:06 ` [f2fs-dev] " Eric Biggers
2021-08-18 0:06 ` Eric Biggers
2021-08-20 9:35 ` Chao Yu
2021-08-20 9:35 ` [f2fs-dev] " Chao Yu
2021-08-20 18:11 ` Eric Biggers
2021-08-20 18:11 ` Eric Biggers
2021-08-20 22:01 ` [f2fs-dev] " Chao Yu
2021-08-20 22:01 ` Chao Yu
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