From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5F02418787F; Mon, 15 Jul 2024 12:25:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721046356; cv=none; b=NH5VRaPh4QI7DpQwrsW+uPEokRDw5e42/vy70QCJcv49kdXnOYQH3UztYybCdpcqCeMegn/rHm76nYtRAcPmsiRNADW0cdytgjzqh2Y2GmhGQTAOm48fXyUBfWFc+eZhMjfweky1DjSGVmGtfqSMwzhoXS3MXL2i81TxqBNuS7A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721046356; c=relaxed/simple; bh=ljU/zTyYsCLzTYt08UP6MIU1t99CrcH9Dh+yt1J8Jug=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=cXqvbdC+iT5hIuZhGNvRvMhXdC47XkIjbJpZ4/a22ZBl7WjThbFC60V5eHqvQtyzRAwzmZ1gZy31p2PLAdoO7VdvY4M/PDFouqSYqOw0ZAIa6V8Frb42FLoYN7CgM9pIGmDZrcieG6LWOn3Z9CyPgunoxO4CIep9zpU/zuI2LaQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DwD7nGYk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DwD7nGYk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 40E3EC32782; Mon, 15 Jul 2024 12:25:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1721046356; bh=ljU/zTyYsCLzTYt08UP6MIU1t99CrcH9Dh+yt1J8Jug=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=DwD7nGYkHlXKdXAQGUp8lN8mzurYVc/qxbckO40SsptkloSr3tHMv1NFJM0GUN4qK qN0e47V9PTiLgbh01+WCjkADgDasHULPtoYvTvXD84P1Vd1BIsfrz4FlkkDixagNms SvFuYZ1ewD01LbfPPO1z9Zta4ZzCinBuEOOKxN+pqSbJ5NAnf+QjbXEXVX3BX34s0v 4qzFUNwTy+QWfevPjwm1kALX0AonDcG38h9a9HzUpNFU5A32/xzAFkuOVXo/CXerE3 UpcDwOLRlocma/DUDcgWW4qS7y7zp14pWlWhpu7GWentp3zQmvtQONeeBIu05M97Pl URHm1quN+rr7A== Message-ID: <85dcb63bd31b962039269bef6e3791c82cef9ecb.camel@kernel.org> Subject: Re: [PATCH] nfsd: remove unneeded EEXIST error check in nfsd_do_file_acquire From: Jeff Layton To: NeilBrown Cc: Chuck Lever , Olga Kornievskaia , Dai Ngo , Tom Talpey , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, Youzhong Yang Date: Mon, 15 Jul 2024 08:25:53 -0400 In-Reply-To: <172100324023.15471.746980048334211968@noble.neil.brown.name> References: <20240711-nfsd-next-v1-1-f9f944500503@kernel.org> <172100324023.15471.746980048334211968@noble.neil.brown.name> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv 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linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-07-15 at 10:27 +1000, NeilBrown wrote: > On Fri, 12 Jul 2024, Jeff Layton wrote: > > Given that we do the search and insertion while holding the i_lock, I > > don't think it's possible for us to get EEXIST here. Remove this case. >=20 > I was going to comment that as rhltable_insert() cannot return -EEXIST > that is an extra reason to discard the check. But then I looked at the > code an I cannot convince myself that it cannot. > If __rhashtable_insert_fast() finds that tbl->future_tbl is not NULL it > calls rhashtable_insert_slow(), and that seems to fail if the key > already exists. But it shouldn't for an rhltable, it should just add > the new item to the linked list for that key. >=20 > It looks like this has always been broken: adding to an rhltable during > a resize event can cause EEXIST.... >=20 > Would anyone like to check my work? I'm surprise that hasn't been > noticed if it is really the case. >=20 >=20 I don't know this code well at all, but it looks correct to me: static void *rhashtable_try_insert(struct rhashtable *ht, const void *key, struct rhash_head *obj) { struct bucket_table *new_tbl; struct bucket_table *tbl; struct rhash_lock_head __rcu **bkt; unsigned long flags; unsigned int hash; void *data; new_tbl =3D rcu_dereference(ht->tbl); do { tbl =3D new_tbl; hash =3D rht_head_hashfn(ht, tbl, obj, ht->p); if (rcu_access_pointer(tbl->future_tbl)) /* Failure is OK */ bkt =3D rht_bucket_var(tbl, hash); else bkt =3D rht_bucket_insert(ht, tbl, hash); if (bkt =3D=3D NULL) { new_tbl =3D rht_dereference_rcu(tbl->future_tbl, ht= ); data =3D ERR_PTR(-EAGAIN); } else { flags =3D rht_lock(tbl, bkt); data =3D rhashtable_lookup_one(ht, bkt, tbl, hash, key, obj); new_tbl =3D rhashtable_insert_one(ht, bkt, tbl, hash, obj, data); if (PTR_ERR(new_tbl) !=3D -EEXIST) data =3D ERR_CAST(new_tbl); rht_unlock(tbl, bkt, flags); } } while (!IS_ERR_OR_NULL(new_tbl)); if (PTR_ERR(data) =3D=3D -EAGAIN) data =3D ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?: -EAGAIN); return data; } I'm assuming the part we need to worry about is where rhashtable_insert_one returns -EEXIST. It holds the rht_lock across the lookup and insert though. So if rhashtable_insert_one returns -EEXIST, then "data" must be something valid. In that case, "data" won't be overwritten and it will fall through and return the pointer to the entry already there. That said, this logic is really convoluted, so I may have missed something too. > >=20 > > Cc: Youzhong Yang > > Fixes: c6593366c0bf ("nfsd: don't kill nfsd_files because of lease brea= k error") > > Signed-off-by: Jeff Layton > > --- > > This is replacement for PATCH 1/3 in the series I sent yesterday. I > > think it makes sense to just eliminate this case. > > --- > > fs/nfsd/filecache.c | 2 -- > > 1 file changed, 2 deletions(-) > >=20 > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > > index f84913691b78..b9dc7c22242c 100644 > > --- a/fs/nfsd/filecache.c > > +++ b/fs/nfsd/filecache.c > > @@ -1038,8 +1038,6 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, stru= ct svc_fh *fhp, > > if (likely(ret =3D=3D 0)) > > goto open_file; > > =20 > > - if (ret =3D=3D -EEXIST) > > - goto retry; > > trace_nfsd_file_insert_err(rqstp, inode, may_flags, ret); > > status =3D nfserr_jukebox; > > goto construction_err; > >=20 > > --- > > base-commit: ec1772c39fa8dd85340b1a02040806377ffbff27 > > change-id: 20240711-nfsd-next-c9d17f66e2bd > >=20 > > Best regards, > > --=20 > > Jeff Layton > >=20 > >=20 >=20 --=20 Jeff Layton