On Wed 26-02-20 17:02:18, Ritesh Harjani wrote: > > > On 2/25/20 5:38 PM, Jan Kara wrote: > > Lockdep complains about a chain: > > sb_internal#2 --> &ei->xattr_sem#2 --> fs_reclaim > > > > and shrink_dentry_list -> ext2_evict_inode -> ext2_xattr_delete_inode -> > > down_write(ei->xattr_sem) creating a locking cycle in the reclaim path. > > This is however a false positive because when we are in > > ext2_evict_inode() we are the only holder of the inode reference and > > nobody else should touch xattr_sem of that inode. So we cannot ever > > block on acquiring the xattr_sem in the reclaim path. > > > > Silence the lockdep warning by using down_write_trylock() in > > ext2_xattr_delete_inode() to not create false locking dependency. > > > > Reported-by: "J. R. Okajima" <hooanon05g@xxxxxxxxx> > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > Agreed with evict() will only be called when it's the last reference going > down and so we won't be blocked on xattr_sem. > Thanks for clearly explaining the problem in the cover letter. > > Reviewed-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx> Thanks for review! I've now pushed the patch to my tree. Honza > > > > --- > > fs/ext2/xattr.c | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > Changes since v1: > > - changed WARN_ON to WARN_ON_ONCE > > > > diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c > > index 0456bc990b5e..9ad07c7ef0b3 100644 > > --- a/fs/ext2/xattr.c > > +++ b/fs/ext2/xattr.c > > @@ -790,7 +790,15 @@ ext2_xattr_delete_inode(struct inode *inode) > > struct buffer_head *bh = NULL; > > struct ext2_sb_info *sbi = EXT2_SB(inode->i_sb); > > > > - down_write(&EXT2_I(inode)->xattr_sem); > > + /* > > + * We are the only ones holding inode reference. The xattr_sem should > > + * better be unlocked! We could as well just not acquire xattr_sem at > > + * all but this makes the code more futureproof. OTOH we need trylock > > + * here to avoid false-positive warning from lockdep about reclaim > > + * circular dependency. > > + */ > > + if (WARN_ON_ONCE(!down_write_trylock(&EXT2_I(inode)->xattr_sem))) > > + return; > > if (!EXT2_I(inode)->i_file_acl) > > goto cleanup; > > > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
