Messages in this thread | | | Date | Tue, 19 Dec 2023 10:29:08 +0800 | Subject | Re: [PATCH 3/4] ext4: avoid bb_free and bb_fragments inconsistency in mb_free_blocks() | From | Baokun Li <> |
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On 2023/12/18 23:14, Jan Kara wrote: > On Mon 18-12-23 22:18:13, Baokun Li wrote: >> After updating bb_free in mb_free_blocks, it is possible to return without >> updating bb_fragments because the block being freed is found to have >> already been freed, which leads to inconsistency between bb_free and >> bb_fragments. >> >> Since the group may be unlocked in ext4_grp_locked_error(), this can lead >> to problems such as dividing by zero when calculating the average fragment >> length. Therefore, to ensure consistency, move the update of bb_free to >> after the block double-free check. >> >> Fixes: eabe0444df90 ("ext4: speed-up releasing blocks on commit") >> CC: stable@vger.kernel.org # 3.10 >> Signed-off-by: Baokun Li <libaokun1@huawei.com> > I agree there's no point in updating the allocation info if the bitmap is > corrupted. We will not try to allocate (or free) blocks in that group > anymore. I'm just a bit unsure about the EXT4_FC_REPLAY state where we > don't mark the bitmap as corrupted although some blocks were already marked > as freed. So in this case the free space statistics tracking will go > permanently wrong. I'm kind of wondering in which case does fast-commit > free already freed blocks. Ted, any idea? > > Honza Some additional information, this judgment was introduced in commit 8016e29f4362 ("ext4: fast commit recovery path") in v5.10-rc1, at which point mb_regenerate_buddy() was called to regenerate the buddy when it was found to be freeing a block that had already been freed, so there was no problem. Until v5.11-rc1 commit 6bd97bf273bd ("ext4: remove redundant mb_regenerate_buddy()") removes the logic to regenerate the buddy, it looks like the free space statistics will remain wrong. If this normal scenario exists, perhaps buddy should be regenerated here?
Thanks, Baokun >> --- >> fs/ext4/mballoc.c | 13 ++++++------- >> 1 file changed, 6 insertions(+), 7 deletions(-) >> >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c >> index a95fa6e2b0f9..2fbee0f0f5c3 100644 >> --- a/fs/ext4/mballoc.c >> +++ b/fs/ext4/mballoc.c >> @@ -1892,11 +1892,6 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, >> mb_check_buddy(e4b); >> mb_free_blocks_double(inode, e4b, first, count); >> >> - this_cpu_inc(discard_pa_seq); >> - e4b->bd_info->bb_free += count; >> - if (first < e4b->bd_info->bb_first_free) >> - e4b->bd_info->bb_first_free = first; >> - >> /* access memory sequentially: check left neighbour, >> * clear range and then check right neighbour >> */ >> @@ -1922,9 +1917,14 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, >> sb, e4b->bd_group, >> EXT4_GROUP_INFO_BBITMAP_CORRUPT); >> } >> - goto done; >> + return; >> } >> >> + this_cpu_inc(discard_pa_seq); >> + e4b->bd_info->bb_free += count; >> + if (first < e4b->bd_info->bb_first_free) >> + e4b->bd_info->bb_first_free = first; >> + >> /* let's maintain fragments counter */ >> if (left_is_free && right_is_free) >> e4b->bd_info->bb_fragments--; >> @@ -1949,7 +1949,6 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b, >> if (first <= last) >> mb_buddy_mark_free(e4b, first >> 1, last >> 1); >> >> -done: >> mb_set_largest_free_order(sb, e4b->bd_info); >> mb_update_avg_fragment_size(sb, e4b->bd_info); >> mb_check_buddy(e4b); >> -- >> 2.31.1 >>
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