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 270BF1DB122; Mon, 21 Apr 2025 12:00:21 +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=1745236821; cv=none; b=aIJJ+HQrqokyLQcGP3h+TtdTgO0j3PsL86o1wh3nmMpU+c2rDEGsD2PkUe0sUeRehnPhvUYk8yR6EscZEEowqcBRAGxahrP/I8Ltp4/7QVCjZ4MTuT2dvWut2cmjn3jcfwU2Lu/epQhi8WYLQZ0NnirGaMuB8dQPVkY+KY5dnT8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745236821; c=relaxed/simple; bh=W9NOrm9S/k4sk/Uv/kYF+L5FLMLUi7wpa+sanI+asWI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=B77crgVcbxWw6bfv16mZOCCanuTwjR2NLL63dlG7Zkf0EfgpDkQToNKykVsoWjQWIuiAD4cjW8taVcX6eiYmswM/8MYnYo0aCG3FC0R39UPPv9IHFfzEKwkysNPmhu/tOTiNxU1g4GHnLYOe8T2Euzc4RKSIyqmQo3Z6edku3H4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rdxgVY7u; 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="rdxgVY7u" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC295C4CEE4; Mon, 21 Apr 2025 12:00:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745236820; bh=W9NOrm9S/k4sk/Uv/kYF+L5FLMLUi7wpa+sanI+asWI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=rdxgVY7u4Wr/0ynkCmkzMWC9eIclSz+fmcOILcMHqoAMnCEfqOWaWloopBHaHq7YY d+up9T280tE01YvHzaXZGcCSl8CjWIruElG3ZXlTN4Yz1pa53kle/oBv6DX2CcuHLl s564wE1au2JwXnH/k9yO2xETnaafhY0EXazkxCsKsXmHC3ciAjwTNhFJCfmS+dWW5k MicdH8ClN+qVhwCKYOftTkl/cSYdWJqIL+ypylMJdyaFlGqJXELTpJz1Ckf/agdujW Yo8RVgoGapErDwSow91+gdmDTwyhfNid5YSmOPom1ZleID+gvzW8j11ZVY+OP182vh S4zgDub2bkTUw== Message-ID: <3452e3fea7c250fc0816aa1b55f579849e056283.camel@kernel.org> Subject: Re: [PATCH 2/2] nfs: handle failure of get_nfs_open_context From: Jeff Layton To: Li Lingfeng , trondmy@kernel.org, anna@kernel.org, bcodding@redhat.com Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai1@huaweicloud.com, houtao1@huawei.com, yi.zhang@huawei.com, yangerkun@huawei.com, lilingfeng@huaweicloud.com Date: Mon, 21 Apr 2025 08:00:18 -0400 In-Reply-To: <40d40603-f9a9-4eaa-aaa6-d5ce31445aa4@huawei.com> References: <20250419085355.1451457-1-lilingfeng3@huawei.com> <20250419085355.1451457-3-lilingfeng3@huawei.com> <828b70d9f1c0a34966aeda8198d80046dcd2bba2.camel@kernel.org> <40d40603-f9a9-4eaa-aaa6-d5ce31445aa4@huawei.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; 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text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.3 (3.54.3-1.fc41) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-04-21 at 09:56 +0800, Li Lingfeng wrote: > =E5=9C=A8 2025/4/19 20:34, Jeff Layton =E5=86=99=E9=81=93: > > On Sat, 2025-04-19 at 16:53 +0800, Li Lingfeng wrote: > > > During initialization of unlockdata or lockdata structures, if acquir= ing > > > the nfs_open_context fails, the current operation must be aborted to > > > ensure the nfs_open_context remains valid after initialization comple= tes. > > > This is critical because both lock and unlock release callbacks > > > dereference the nfs_open_context - an invalid context could lead to n= ull > > > pointer dereference. > > >=20 > > > Fixes: faf5f49c2d9c ("NFSv4: Make NFS clean up byte range locks async= hronously") > > > Fixes: a5d16a4d090b ("NFSv4: Convert LOCK rpc call into an asynchrono= us RPC call") > > > Signed-off-by: Li Lingfeng > > > --- > > > fs/nfs/nfs4proc.c | 22 +++++++++++++++------- > > > 1 file changed, 15 insertions(+), 7 deletions(-) > > >=20 > > > diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c > > > index 9f5689c43a50..d76cf0f79f9c 100644 > > > --- a/fs/nfs/nfs4proc.c > > > +++ b/fs/nfs/nfs4proc.c > > > @@ -7075,24 +7075,27 @@ static struct nfs4_unlockdata *nfs4_alloc_unl= ockdata(struct file_lock *fl, > > > struct nfs4_state *state =3D lsp->ls_state; > > > struct inode *inode =3D state->inode; > > > struct nfs_lock_context *l_ctx; > > > + struct nfs_open_context *open_ctx; > > > =20 > > > p =3D kzalloc(sizeof(*p), GFP_KERNEL); > > > if (p =3D=3D NULL) > > > return NULL; > > > l_ctx =3D nfs_get_lock_context(ctx); > > > - if (!IS_ERR(l_ctx)) { > > > + if (!IS_ERR(l_ctx)) > > > p->l_ctx =3D l_ctx; > > > - } else { > > > - kfree(p); > > > - return NULL; > > > - } > > > + else > > > + goto out_free; > > > + /* Ensure we don't close file until we're done freeing locks! */ > > > + open_ctx =3D get_nfs_open_context(ctx); > > >=20 > > >=20 > > Sorry for the confusion. Now that I look more closely, I think I was > > wrong before. > >=20 > > This can't fail, because the caller holds a reference to ctx, so the > > refcount must be non-zero. Instead of this patch, could you add a > > comment in there to that effect to make this clear in the future? > Hi Jeff, >=20 > Thank you for the feedback. > Adding a comment instead of this patch may be better. >=20 > However, I=E2=80=99d like to seek your guidance on a broader question: Fo= r > scenarios where an error condition =E2=80=8Bcurrently cannot occur but wo= uld lead > to severe consequences (e.g., NULL pointer dereference, data corruption) > if it ever did happen (e.g., due to future code changes or bugs), do you > recommend proactively adding error handling as a defensive measure? >=20 > My rationale: > =E2=80=8BCurrent code: No code path triggers this condition today --> Han= dling > code would be "dead" for now. > =E2=80=8BFuture risks: If a bug introduced later allows the condition to = occur, > silent failure or crashes could result. > Is there a kernel/dev policy on such preemptive safeguards? Or should we > address these only when the triggering scenarios materialize? >=20 > Your insight would help me align with the project=E2=80=99s practices. > Thanks in advance! >=20 There is no firm policy here. We just have to make a judgment call in these situations. In general, we don't want to litter the code with a lot of conditionals or BUG_ONs/WARN_ONs for cases that can really never happen, as that might slow things down for little benefit, and it makes the code less readable. OTOH, being proactive about catching errors is a good thing, so if there is any chance that things could change in the future, it's good to have a warning about it. In this particular case, given that we have to hold a reference in order to pass a pointer to the ctx in the first place, there is little value in doing (e.g.) WARN_ON(!open_ctx), as that should really never happen. > Best regards, > Lingfeng > >=20 > >=20 > > > + if (open_ctx) > > > + p->ctx =3D open_ctx; > > > + else > > > + goto out_free; > > If we did decide to keep the error handling however, this would leak > > l_ctx. That reference would also need to be put if open_ctx was NULL > > here. > >=20 > > > p->arg.fh =3D NFS_FH(inode); > > > p->arg.fl =3D &p->fl; > > > p->arg.seqid =3D seqid; > > > p->res.seqid =3D seqid; > > > p->lsp =3D lsp; > > > - /* Ensure we don't close file until we're done freeing locks! */ > > > - p->ctx =3D get_nfs_open_context(ctx); > > > locks_init_lock(&p->fl); > > > locks_copy_lock(&p->fl, fl); > > > p->server =3D NFS_SERVER(inode); > > > @@ -7100,6 +7103,9 @@ static struct nfs4_unlockdata *nfs4_alloc_unloc= kdata(struct file_lock *fl, > > > nfs4_stateid_copy(&p->arg.stateid, &lsp->ls_stateid); > > > spin_unlock(&state->state_lock); > > > return p; > > > +out_free: > > > + kfree(p); > > > + return NULL; > > > } > > > =20 > > > static void nfs4_locku_release_calldata(void *data) > > > @@ -7327,6 +7333,8 @@ static struct nfs4_lockdata *nfs4_alloc_lockdat= a(struct file_lock *fl, > > > p->lsp =3D lsp; > > > p->server =3D server; > > > p->ctx =3D get_nfs_open_context(ctx); > > > + if (!p->ctx) > > > + goto out_free_seqid; > > > locks_init_lock(&p->fl); > > > locks_copy_lock(&p->fl, fl); > > > return p; --=20 Jeff Layton