Messages in this thread | | | Date | Mon, 29 Apr 2019 19:54:06 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH 1/2] f2fs: fix to avoid potential negative .f_bfree |
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On 04/29, Chao Yu wrote: > On 2019-4-28 21:47, Jaegeuk Kim wrote: > > On 04/26, Chao Yu wrote: > >> When calculating .f_bfree value in f2fs_statfs(), sbi->unusable_block_count > >> can be increased after the judgment condition, result in overflow of > >> .f_bfree in later calculation. This patch fixes to use a temporary signed > >> variable to save the calculation result of .f_bfree. > >> > >> if (unlikely(buf->f_bfree <= sbi->unusable_block_count)) > >> buf->f_bfree = 0; > >> else > >> buf->f_bfree -= sbi->unusable_block_count; > > > > Do we just need stat_lock for this? > > Like we access other stat value in statfs(), we just need the instantaneous > value of .unusable_block_count, so we don't need additional stat_lock, right?
What I've concerend is whether or not this fixes all the inconsistent values. The original intention was providing stats in best effort, so we wouldn't use any lock.
> > Thanks, > > > > >> > >> Signed-off-by: Chao Yu <yuchao0@huawei.com> > >> --- > >> fs/f2fs/super.c | 7 +++++-- > >> 1 file changed, 5 insertions(+), 2 deletions(-) > >> > >> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > >> index 2376bb01b5c4..fcc9793dbc2c 100644 > >> --- a/fs/f2fs/super.c > >> +++ b/fs/f2fs/super.c > >> @@ -1216,6 +1216,7 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf) > >> u64 id = huge_encode_dev(sb->s_bdev->bd_dev); > >> block_t total_count, user_block_count, start_count; > >> u64 avail_node_count; > >> + long long bfree; > >> > >> total_count = le64_to_cpu(sbi->raw_super->block_count); > >> user_block_count = sbi->user_block_count; > >> @@ -1226,10 +1227,12 @@ static int f2fs_statfs(struct dentry *dentry, struct kstatfs *buf) > >> buf->f_blocks = total_count - start_count; > >> buf->f_bfree = user_block_count - valid_user_blocks(sbi) - > >> sbi->current_reserved_blocks; > >> - if (unlikely(buf->f_bfree <= sbi->unusable_block_count)) > >> + > >> + bfree = buf->f_bfree - sbi->unusable_block_count; > >> + if (unlikely(bfree < 0)) > >> buf->f_bfree = 0; > >> else > >> - buf->f_bfree -= sbi->unusable_block_count; > >> + buf->f_bfree = bfree; > >> > >> if (buf->f_bfree > F2FS_OPTION(sbi).root_reserved_blocks) > >> buf->f_bavail = buf->f_bfree - > >> -- > >> 2.18.0.rc1
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