On Wed, Sep 30, 2015 at 11:06 AM, Zhao Lei <zhaolei@xxxxxxxxxxxxxx> wrote: > Hi, Filipe Manana > >> -----Original Message----- >> From: linux-btrfs-owner@xxxxxxxxxxxxxxx >> [mailto:linux-btrfs-owner@xxxxxxxxxxxxxxx] On Behalf Of Filipe Manana >> Sent: Wednesday, September 30, 2015 3:43 PM >> To: Zhao Lei <zhaolei@xxxxxxxxxxxxxx> >> Cc: linux-btrfs@xxxxxxxxxxxxxxx >> Subject: Re: [PATCH 1/2] btrfs: Fix lost-data-profile caused by auto removing bg >> >> On Tue, Sep 29, 2015 at 2:51 PM, Zhao Lei <zhaolei@xxxxxxxxxxxxxx> wrote: >> > Reproduce: >> > (In integration-4.3 branch) >> > >> > TEST_DEV=(/dev/vdg /dev/vdh) >> > TEST_DIR=/mnt/tmp >> > >> > umount "$TEST_DEV" >/dev/null >> > mkfs.btrfs -f -d raid1 "${TEST_DEV[@]}" >> > >> > mount -o nospace_cache "$TEST_DEV" "$TEST_DIR" >> > umount "$TEST_DEV" >> > >> > mount -o nospace_cache "$TEST_DEV" "$TEST_DIR" >> > btrfs filesystem usage $TEST_DIR >> > >> > We can see the data chunk changed from raid1 to single: >> > # btrfs filesystem usage $TEST_DIR >> > Data,single: Size:8.00MiB, Used:0.00B >> > /dev/vdg 8.00MiB >> > # >> > >> > Reason: >> > When a empty filesystem mount with -o nospace_cache, the last data >> > blockgroup will be auto-removed in umount. >> > >> > Then if we mount it again, there is no data chunk in the filesystem, >> > so the only available data profile is 0x0, result is all new chunks >> > are created as single type. >> > >> > Fix: >> > Don't auto-delete last blockgroup for a raid type. >> > >> > Test: >> > Test by above script, and confirmed the logic by debug output. >> > >> > Signed-off-by: Zhao Lei <zhaolei@xxxxxxxxxxxxxx> >> > --- >> > fs/btrfs/extent-tree.c | 3 ++- >> > 1 file changed, 2 insertions(+), 1 deletion(-) >> > >> > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index >> > 79a5bd9..3505649 100644 >> > --- a/fs/btrfs/extent-tree.c >> > +++ b/fs/btrfs/extent-tree.c >> > @@ -10012,7 +10012,8 @@ void btrfs_delete_unused_bgs(struct >> btrfs_fs_info *fs_info) >> > bg_list); >> > space_info = block_group->space_info; >> > list_del_init(&block_group->bg_list); >> > - if (ret || btrfs_mixed_space_info(space_info)) { >> > + if (ret || btrfs_mixed_space_info(space_info) || >> > + block_group->list.next == block_group->list.prev) >> > + { >> >> This isn't race free. The list block_group->list is protected by the groups_sem >> semaphore. Need to take before doing this check. > > Thanks for pointing out this. > >> You can do that in the "if" statement below this one, where we're holding >> &space_info->groups_sem [1] >> > It is hard to do check in btrfs_remove_block_group(), because it is common > function used by both balance and auto-remove bg. I didn't say to move it to or touch btrfs_remove_block_group() at all. What I meant is to do check still inside btrfs_delete_unused_bgs but in the other "if" statement that is done while holding the groups semaphore, i.e.: diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 9f96042..627ac3b 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -10022,7 +10022,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) spin_lock(&block_group->lock); if (block_group->reserved || btrfs_block_group_used(&block_group->item) || - block_group->ro) { + block_group->ro || + lock_group->list.next == block_group->list.prev) { /* * We want to bail if we made new allocations or have * outstanding allocations in this block group. We do > > For balance operation, we can remove lattest bg in some case, or we need > add additional argument to separate these two operation(complex). > > So I decided to take groups_sem semaphore in place of checking. Not sure I follow. The problem I was pointing is doing the check without holding the groups semaphore. > Thanks for notice this lock problem. > > btw, could I add your signed-off-by or reviewed-by in patch 2/2? Yeah, once I see the updated version I can add a reviewed-by tag. thanks > > Thanks > Zhaolei > >> thanks >> >> [1] >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/exte >> nt-tree.c?id=refs/tags/v4.3-rc3#n10021 >> >> > btrfs_put_block_group(block_group); >> > continue; >> > } >> > -- >> > 1.8.5.1 >> > >> > -- >> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" >> > in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo >> > info at http://vger.kernel.org/majordomo-info.html >> >> >> >> -- >> Filipe David Manana, >> >> "Reasonable men adapt themselves to the world. >> Unreasonable men adapt the world to themselves. >> That's why all progress depends on unreasonable men." >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body >> of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at >> http://vger.kernel.org/majordomo-info.html > -- Filipe David Manana, "Reasonable men adapt themselves to the world. Unreasonable men adapt the world to themselves. That's why all progress depends on unreasonable men." -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
