linux-kernel - Re: [f2fs-dev] [PATCH 1/3] f2fs: turn off atomic writes when deteting abnormal behaviors

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Message-ID: <20180727091721.GA16155@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Fri, 27 Jul 2018 18:17:21 +0900
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/3] f2fs: turn off atomic writes when
 deteting abnormal behaviors

On 07/23, Chao Yu wrote:
> On 2018/7/23 21:03, Jaegeuk Kim wrote:
> > On 07/16, Chao Yu wrote:
> >> On 2018/7/15 9:11, Jaegeuk Kim wrote:
> >>> In order to prevent abusing atomic writes by abnormal users, we've added a
> >>> threshold, 20% over memory footprint, which disallows further atomic writes.
> >>> Previously, however, SQLite doesn't know the files became normal, so that
> >>> it could write stale data and commit on revoked normal database file.
> >>>
> >>> Once f2fs detects such the abnormal behavior, this patch simply disables
> >>> all the atomic operations such as:
> >>> - write_begin() gives EINVAL to avoid stale data writes, and SQLite will call
> >>>   F2FS_IOC_ABORT_VOLATILE_WRITE to notify aborting the transaction,
> >>> - F2FS_IOC_START_ATOMIC_WRITE gives EINVAL for SQLite to fall back normal
> >>>   journal_mode,
> >>> - F2FS_IOC_COMMIT_ATOMIC_WRITE gives EINVAL, if the file was revoked, so that
> >>>   Framework retries to submit the transaction given propagated SQLite error.
> >>>
> >>> Note that, this patch also turns off atomic operations, if foreground GC tries
> >>> to move atomic files too frequently.
> >>
> >> Well, how about just keeping original implementation: shutdown atomic write for
> >> those files which are really affect fggc? Since intention of the original
> >> behavior is targeting to abnormal atomic write usage, e.g. open atomic_write
> >> file for very long time, then fggc will be blocked each time when moving its
> >> block. So shutdown it, fggc will recover.
> > 
> > The point here is stopping sqlite to keep going wrong data writes even after
> > we already revoked blocks.
> 
> Yes, that's correct, what I mean is that if we can do that with smaller
> granularity like just revoke blocks for file which is blocking fggc, it will
> affect system/sqlite flow much less than forcing closing all atomic_write.

How about this?

>From 64d2becb82a496c2e2c04abeed42efa3b401ee20 Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaegeuk@...nel.org>
Date: Fri, 27 Jul 2018 18:15:11 +0900
Subject: [PATCH] f2fs: don't allow any writes on aborted atomic writes

In order to prevent abusing atomic writes by abnormal users, we've added a
threshold, 20% over memory footprint, which disallows further atomic writes.
Previously, however, SQLite doesn't know the files became normal, so that
it could write stale data and commit on revoked normal database file.

Once f2fs detects such the abnormal behavior, this patch tries to avoid further
writes in write_begin().

Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/data.c | 3 ++-
 fs/f2fs/file.c | 7 ++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 22dd00c6e241..02ec2603725f 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2295,7 +2295,8 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 	trace_f2fs_write_begin(inode, pos, len, flags);
 
 	if (f2fs_is_atomic_file(inode) &&
-			!f2fs_available_free_memory(sbi, INMEM_PAGES)) {
+			(is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST) ||
+			!f2fs_available_free_memory(sbi, INMEM_PAGES))) {
 		err = -ENOMEM;
 		drop_atomic = true;
 		goto fail;
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ff2cb8fb6934..c2c47f3248c4 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1708,8 +1708,11 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
 
 	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 
-	if (f2fs_is_atomic_file(inode))
+	if (f2fs_is_atomic_file(inode)) {
+		if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
+			ret = -EINVAL;
 		goto out;
+	}
 
 	ret = f2fs_convert_inline_inode(inode);
 	if (ret)
@@ -1871,6 +1874,8 @@ static int f2fs_ioc_abort_volatile_write(struct file *filp)
 		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
 	}
 
+	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
+
 	inode_unlock(inode);
 
 	mnt_drop_write_file(filp);
-- 
2.17.0.441.gb46fe60e1d-goog