On 2019/11/1 18:30, Brian Foster wrote: > On Fri, Nov 01, 2019 at 03:04:11PM +0800, kaixuxia wrote: >> >> >> On 2019/10/31 20:27, Brian Foster wrote: >>> On Wed, Oct 30, 2019 at 05:49:34PM +0800, kaixuxia wrote: >>>> When target_ip exists in xfs_rename(), the xfs_dir_replace() call may >>>> need to hold the AGF lock to allocate more blocks, and then invoking >>>> the xfs_droplink() call to hold AGI lock to drop target_ip onto the >>>> unlinked list, so we get the lock order AGF->AGI. This would break the >>>> ordering constraint on AGI and AGF locking - inode allocation locks >>>> the AGI, then can allocate a new extent for new inodes, locking the >>>> AGF after the AGI. >>>> >>>> In this patch we check whether the replace operation need more >>>> blocks firstly. If so, acquire the agi lock firstly to preserve >>>> locking order(AGI/AGF). Actually, the locking order problem only >>>> occurs when we are locking the AGI/AGF of the same AG. For multiple >>>> AGs the AGI lock will be released after the transaction committed. >>>> >>>> Signed-off-by: kaixuxia <kaixuxia@xxxxxxxxxxx> >>>> --- >>>> fs/xfs/libxfs/xfs_dir2.c | 30 ++++++++++++++++++++++++++++++ >>>> fs/xfs/libxfs/xfs_dir2.h | 2 ++ >>>> fs/xfs/xfs_inode.c | 14 ++++++++++++++ >>>> 3 files changed, 46 insertions(+) >>>> >>>> diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c >>>> index 867c5de..9d9ae16 100644 >>>> --- a/fs/xfs/libxfs/xfs_dir2.c >>>> +++ b/fs/xfs/libxfs/xfs_dir2.c >>>> @@ -463,6 +463,36 @@ >>>> } >>>> >>>> /* >>>> + * Check whether the replace operation need more blocks. Ignore >>>> + * the parameters check since the real replace() call below will >>>> + * do that. >>>> + */ >>>> +bool >>>> +xfs_dir_replace_needblock( >>>> + struct xfs_inode *dp, >>>> + xfs_ino_t inum) >>>> +{ >>>> + int newsize; >>>> + xfs_dir2_sf_hdr_t *sfp; >>>> + >>>> + /* >>>> + * Only convert the shortform directory to block form maybe need >>>> + * more blocks. >>>> + */ >>>> + if (dp->i_d.di_format != XFS_DINODE_FMT_LOCAL) >>>> + return false; >>>> + >>>> + sfp = (xfs_dir2_sf_hdr_t *)dp->i_df.if_u1.if_data; >>>> + newsize = dp->i_df.if_bytes + (sfp->count + 1) * XFS_INO64_DIFF; >>>> + >>>> + if (inum > XFS_DIR2_MAX_SHORT_INUM && >>>> + sfp->i8count == 0 && newsize > XFS_IFORK_DSIZE(dp)) >>>> + return true; >>>> + else >>>> + return false; >>>> +} >>>> + >>> >>> It's slightly unfortunate we need to do these kind of double checks, but >>> it seems reasonable enough as an isolated fix. From a factoring >>> standpoint, it might be a little cleaner to move this down in >>> xfs_dir2_sf.c as an xfs_dir2_sf_replace_needblock() helper, actually use >>> it in the xfs_dir2_sf_replace() function where these checks are >>> currently open coded and then export it so we can call it in the higher >>> level function as well for the locking fix. >>> >> Yeah, makes more sense. Also maybe we could add a function helper like >> the xfs_dir_canenter() call, it just check whether the replace operation >> need more blocks, >> >> int xfs_dir_replace_needblock(...) >> { >> xfs_dir_replace(tp, dp, name, 0, 0); >> } >> >> I'm not sure if this approach is reasonable... >> > > I thought we were attempting to get rid of those calls, but I could be > mistaken. > Yeah, just like what you said, we can call it in the higher level function. >> Actually, there are some different solutions for the locking fix. One solution >> is checking whether the replace operation need more blocks and acquiring AGI >> lock before AGF lock. Another one is moving xfs_droplink() call to before the >> xfs_dir_replace() call, but this solution may not be suitable. The third one >> is expanding the directory in one transaction, but I'm not sure about this >> solution and have no idea how to do it... >> Comments about these solutions, which one is more reasonable? >> > > I'm not sure we want to split things up into multiple transactions (if > that's what you mean by the third option) because then we could be at > risk of creating an inconsistent state in the event of a crash. > Reordering the calls is cleaner in some respect because it doesn't > require any new code, but it would probably require a closer look to > make sure we don't create a problematic state for the current code in > any way (i.e. processing a directory entry of an already unlinked > inode). This patch requires some extra code, but it's the most simple > solution from a logical standpoint. If you want my .02, I think either > of the first two options are reasonable (provided they are correct). > Perhaps others have stronger opinions or other ideas... > Thanks for your comments. I will continue to use the approach in this patch, and sent the V2 patch to address the comments. Kaixu > Brian > >> kaixu >> >>> Brian >>> >>>> +/* >>>> * Replace the inode number of a directory entry. >>>> */ >>>> int >>>> diff --git a/fs/xfs/libxfs/xfs_dir2.h b/fs/xfs/libxfs/xfs_dir2.h >>>> index f542447..e436c14 100644 >>>> --- a/fs/xfs/libxfs/xfs_dir2.h >>>> +++ b/fs/xfs/libxfs/xfs_dir2.h >>>> @@ -124,6 +124,8 @@ extern int xfs_dir_lookup(struct xfs_trans *tp, struct xfs_inode *dp, >>>> extern int xfs_dir_removename(struct xfs_trans *tp, struct xfs_inode *dp, >>>> struct xfs_name *name, xfs_ino_t ino, >>>> xfs_extlen_t tot); >>>> +extern bool xfs_dir_replace_needblock(struct xfs_inode *dp, >>>> + xfs_ino_t inum); >>>> extern int xfs_dir_replace(struct xfs_trans *tp, struct xfs_inode *dp, >>>> struct xfs_name *name, xfs_ino_t inum, >>>> xfs_extlen_t tot); >>>> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c >>>> index 18f4b26..c239070 100644 >>>> --- a/fs/xfs/xfs_inode.c >>>> +++ b/fs/xfs/xfs_inode.c >>>> @@ -3196,6 +3196,7 @@ struct xfs_iunlink { >>>> struct xfs_trans *tp; >>>> struct xfs_inode *wip = NULL; /* whiteout inode */ >>>> struct xfs_inode *inodes[__XFS_SORT_INODES]; >>>> + struct xfs_buf *agibp; >>>> int num_inodes = __XFS_SORT_INODES; >>>> bool new_parent = (src_dp != target_dp); >>>> bool src_is_directory = S_ISDIR(VFS_I(src_ip)->i_mode); >>>> @@ -3361,6 +3362,19 @@ struct xfs_iunlink { >>>> * In case there is already an entry with the same >>>> * name at the destination directory, remove it first. >>>> */ >>>> + >>>> + /* >>>> + * Check whether the replace operation need more blocks. >>>> + * If so, acquire the agi lock firstly to preserve locking >>>> + * order(AGI/AGF). >>>> + */ >>>> + if (xfs_dir_replace_needblock(target_dp, src_ip->i_ino)) { >>>> + error = xfs_read_agi(mp, tp, >>>> + XFS_INO_TO_AGNO(mp, target_ip->i_ino), &agibp); >>>> + if (error) >>>> + goto out_trans_cancel; >>>> + } >>>> + >>>> error = xfs_dir_replace(tp, target_dp, target_name, >>>> src_ip->i_ino, spaceres); >>>> if (error) >>>> -- >>>> 1.8.3.1 >>>> >>> >> >> -- >> kaixuxia > -- kaixuxia