From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 725E6443C19 for ; Mon, 12 Oct 2026 12:00:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791806405; cv=none; b=IvdpModPRmRrMhW/p0bzDATeeTFw3tZUvXu93ZP2/02+6X8MalEflVmF7yvcq3UxY03UJHLZUCfYZJew+o6cyauU9s30TRhuzZJuFi+oUb4Dbf1kal6zG29bugVBUs0QKXEI44LCx359ymKcpf4HQ4GfJwaHHB1HryJN4fTQEYg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791806405; c=relaxed/simple; bh=urd8dWOg4p2ndhFXYDyerzjHfuTEDAf093fOv1G/bOo=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=Y9laB1lR1U2qP5aIwcYk+TCYjTinf2NyNQWhRSeVBwoUu0WOtJd8kAqYCS1jDW1PpK4MIJXnyqrTmq/4YwxDnAdYHhcHRc0W/ShNju0eeP1cnmewYxuAU7JkiaFwrnrSuw2+h6XAVz7bnwLdyVS/rTllStVnV/qhA7GhfQJBRRA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=D2HS+8Fa; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="D2HS+8Fa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 69B9F1F0089B; Mon, 12 Oct 2026 12:00:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791806401; bh=vTOWQiw5/S4LkVSvWolvVXD8QLf3c3kexR7QrITUJwI=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=D2HS+8FaebN5HCe2Cj9CJXeTAxX+3JqMjmARQmudi4LXszq5pZ3lZ9BFl1Q9bnyOg ZbvTpeDpPihFEnorSjJ1dYRkteKBpFlLyBCZ4NwZgfVXDResd4RVhxsdX8nvJyJtnC iDsgvy3ie/kbYGoPVthZg9WWzP57eFmZkI3VvWBnmnW9wYzuve/zhRnPrQTZUxC8mw wHc3tFuwBWkVKALx2JBr1MN1Fv2eo1FSw7xx5as9MfQlQzteTzGZmavi1+weIExvr/ hp8uyMG2jxvAQEuLsUIkS004R/jHPHccq9m24CpfB1+vW8oqDgXH5+OyB7IUDOhuIf H0+go/RDFRGkg== Message-ID: <49d70daa2af39596709614bd04431404a7e515a5.camel@kernel.org> Subject: Re: [PATCH v1] NFSD: Take a file unhashed during construction back off the LRU From: Jeff Layton To: Chuck Lever , NeilBrown , Olga Kornievskaia , Dai Ngo , Tom Talpey Cc: Christian Brauner , linux-nfs@vger.kernel.org Date: Mon, 12 Oct 2026 07:59:58 -0400 In-Reply-To: <20261011205451.96638-1-cel@kernel.org> References: <20261011205451.96638-1-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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inserts a new nfsd_file into the hash table, > opens the file, and only then adds the entry to the LRU. In between, > nfsd_file_cond_queue() can unhash the entry from any caller that > tests GC but not PENDING, such as nfsd_file_queue_for_close(), with > nothing on the LRU to remove. The constructor then calls > nfsd_file_lru_add(), so the entry sits on the LRU with HASHED clear. >=20 > The first laundrette pass after the caller's nfsd_file_put() reaps > the entry. nfsd_file_cache_shutdown_net() purges through the hash > table and misses the entry. With one net namespace, if > nfsd_file_cache_shutdown() runs before that laundrette pass, > list_lru_destroy() runs with the entry still linked, the struct file > stays open, and the export cannot be unmounted. With more than one > net namespace, the entry can outlive its namespace, because nf_net > does not hold a reference. A later laundrette pass then follows a > dangling nf_net pointer in nfsd_file_dispose_list_delayed(). >=20 > A local F_SETLEASE, or nfsd_close_cached_files() on an NFS re-export, > reaches a file under construction when it races an open of the same > inode on another nfsd thread. A process that repeatedly takes and > releases a read lease on an exported file, while an NFSv3 client > reads that file, hits the window on three reads out of four. Before > commit 56221b42d717 ("nfsd: filecache: don't repeatedly add/remove > files on the lru list"), only nfsd_file_put() added an entry to the > LRU, after testing HASHED. >=20 > Test HASHED again after the LRU add. When the bit is clear, take the > entry off the LRU and drop the LRU's reference, so the caller's > nfsd_file_put() frees it. >=20 > Fixes: 56221b42d717 ("nfsd: filecache: don't repeatedly add/remove files = on the lru list") > Assisted-by: https://github.com/brauner/linux-formal > Signed-off-by: Chuck Lever > --- > fs/nfsd/filecache.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) >=20 > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index 42bd8c7859cf..ddca3d580019 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -1311,8 +1311,17 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struc= t net *net, > */ > if (status !=3D nfs_ok || inode->i_nlink =3D=3D 0) > nfsd_file_unhash(nf); > - else if (want_gc) > + else if (want_gc) { > nfsd_file_lru_add(nf); > + /* > + * nfsd_file_cond_queue() can unhash nf before the LRU add. > + * Only one LRU removal succeeds, and that one drops the LRU > + * reference. > + */ > + if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags) && > + nfsd_file_lru_remove(nf)) > + refcount_dec(&nf->nf_ref); > + } > =20 > clear_and_wake_up_bit(NFSD_FILE_PENDING, &nf->nf_flags); > if (status =3D=3D nfs_ok) The problem and solution seem sane. IMO, the comment is not particularly helpful and will be subject to bitrot (what if we change the name of nfsd_file_cond_queue()?). For the code itself though: Reviewed-by: Jeff Layton