From: Al Viro <viro@zeniv.linux.org.uk>
To: Ritesh Harjani <riteshh@linux.ibm.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
wugyuan@cn.ibm.com, jlayton@kernel.org, hsiangkao@aol.com,
Jan Kara <jack@suse.cz>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH RESEND 1/1] vfs: Really check for inode ptr in lookup_fast
Date: Tue, 22 Oct 2019 15:50:53 +0100 [thread overview]
Message-ID: <20191022145053.GY26530@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20191022143736.GX26530@ZenIV.linux.org.uk>
On Tue, Oct 22, 2019 at 03:37:36PM +0100, Al Viro wrote:
> I'm somewhat tempted to make __d_set_inode_and_type() do smp_store_release()
> for setting ->d_flags and __d_entry_type() - smp_load_acquire(); that would
> be pretty much free for x86 (as well as sparc, s390 and itanic) and reasonably
> cheap on ppc and arm64. How badly would e.g. SMP arm suffer from the below
> (completely untested)?
PS: if we really go that way, we'd probably want __d_is_negative(), to be
used only under ->d_lock or with ->d_seq validation.
d_is_negative() callers in fs/dcache.c (all under ->d_lock) as well as
the RCU-side one in lookup_fast() (->d_seq validated) would you that.
Another fun place is do_unlinkat() - there we want to reorder
inode = dentry->d_inode;
if (d_is_negative(dentry))
goto slashes;
As it were, the same race here can lead to unbalanced iput(), if you
hit the window just right.
next prev parent reply other threads:[~2019-10-22 14:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 4:42 [PATCH RESEND 1/1] vfs: Really check for inode ptr in lookup_fast Ritesh Harjani
2019-10-15 4:07 ` Ritesh Harjani
2019-10-22 13:38 ` Ritesh Harjani
2019-10-22 14:37 ` Al Viro
2019-10-22 14:50 ` Al Viro [this message]
2019-10-22 20:11 ` Al Viro
2019-10-23 11:05 ` Ritesh Harjani
2019-11-01 23:46 ` Al Viro
2019-11-02 6:17 ` Al Viro
2019-11-02 17:24 ` Paul E. McKenney
2019-11-02 17:22 ` Paul E. McKenney
2019-11-02 18:08 ` Al Viro
2019-11-03 14:41 ` Paul E. McKenney
2019-11-03 16:35 ` [RFC] lookup_one_len_unlocked() lousy calling conventions Al Viro
2019-11-03 18:20 ` Al Viro
2019-11-03 18:51 ` [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable Al Viro
2019-11-03 19:03 ` [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_parent is not stable either Al Viro
2019-11-13 7:01 ` [PATCH][RFC] ecryptfs_lookup_interpose(): lower_dentry->d_inode is not stable Amir Goldstein
2019-11-13 12:52 ` Al Viro
2019-11-13 16:22 ` Amir Goldstein
2019-11-13 20:18 ` Jean-Louis Biasini
2019-11-03 17:05 ` [PATCH][RFC] ecryptfs unlink/rmdir breakage (similar to caught in ecryptfs rename last year) Al Viro
2019-11-09 3:13 ` [PATCH][RFC] race in exportfs_decode_fh() Al Viro
2019-11-09 16:55 ` Linus Torvalds
2019-11-09 18:26 ` Al Viro
2019-11-11 9:16 ` Christoph Hellwig
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