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[195.231.45.245]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cdce3e4e7sm45045755e9.9.2026.09.01.00.37.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Sep 2026 00:37:04 -0700 (PDT) Message-ID: <3e84c09f-d760-41e9-a99f-0d86239b5ebd@redhat.com> Date: Tue, 1 Sep 2026 09:37:02 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 5/5] tcp: Remove mmap_lock fallback path To: Suren Baghdasaryan , akpm@linux-foundation.org, Eric Dumazet Cc: dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, david@redhat.com, willy@infradead.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, syzbot@syzkaller.appspotmail.com References: <20260831203056.838265-1-surenb@google.com> <20260831203056.838265-6-surenb@google.com> From: Paolo Abeni Content-Language: en-US In-Reply-To: <20260831203056.838265-6-surenb@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit adding Eric. Full series at: https://lore.kernel.org/netdev/20260831203056.838265-1-surenb@google.com/ On 8/31/26 10:30 PM, Suren Baghdasaryan wrote: > From: Dave Hansen > > Previously, the per-VMA locking could fail in the face of writers > which necessitates a fallback to mmap_lock. The new > vma_start_read_unlocked() will wait for writers instead of failing. > > Use the new helper. Wait for writers. Remove the fallback to mmap_lock. > The fallback removal does not affect NOMMU case because TCP_ZEROCOPY > is gated on CONFIG_MMU. > > This really is a nice cleanup. It removes the need to pass the lock > state back and forth to find_tcp_vma(). > > Signed-off-by: Dave Hansen > Acked-by: Lorenzo Stoakes > Acked-by: Vlastimil Babka (SUSE) > Tested-by: syzbot@syzkaller.appspotmail.com > Cc: Andrew Morton > Cc: Liam R. Howlett > Cc: Vlastimil Babka > Cc: Shakeel Butt > Cc: linux-mm@kvack.org > Cc: Greg Kroah-Hartman > Cc: Arve Hjønnevåg > Cc: Todd Kjos > Cc: Christian Brauner > Cc: Carlos Llamas > Cc: Alice Ryhl > Cc: David S. Miller > Cc: David Ahern > Cc: netdev@vger.kernel.org > Signed-off-by: Suren Baghdasaryan > --- > net/ipv4/tcp.c | 31 +++++++++---------------------- > 1 file changed, 9 insertions(+), 22 deletions(-) > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index 455441f1b694..62defe70f3ce 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -2167,27 +2167,18 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk, > } > > static struct vm_area_struct *find_tcp_vma(struct mm_struct *mm, > - unsigned long address, > - bool *mmap_locked) > + unsigned long address) > { > - struct vm_area_struct *vma = lock_vma_under_rcu(mm, address); > + struct vm_area_struct *vma = vma_start_read_unlocked(mm, address); > > - if (vma) { > - if (vma->vm_ops != &tcp_vm_ops) { > - vma_end_read(vma); > - return NULL; > - } > - *mmap_locked = false; > - return vma; > - } > + if (!vma) > + return NULL; > > - mmap_read_lock(mm); > - vma = vma_lookup(mm, address); > - if (!vma || vma->vm_ops != &tcp_vm_ops) { > - mmap_read_unlock(mm); > + if (vma->vm_ops != &tcp_vm_ops) { > + vma_end_read(vma); > return NULL; > } > - *mmap_locked = true; > + > return vma; > } > > @@ -2208,7 +2199,6 @@ static int tcp_zerocopy_receive(struct sock *sk, > u32 seq = tp->copied_seq; > u32 total_bytes_to_map; > int inq = tcp_inq(sk); > - bool mmap_locked; > int ret; > > zc->copybuf_len = 0; > @@ -2233,7 +2223,7 @@ static int tcp_zerocopy_receive(struct sock *sk, > return 0; > } > > - vma = find_tcp_vma(current->mm, address, &mmap_locked); > + vma = find_tcp_vma(current->mm, address); > if (!vma) > return -EINVAL; > > @@ -2315,10 +2305,7 @@ static int tcp_zerocopy_receive(struct sock *sk, > zc, total_bytes_to_map); > } > out: > - if (mmap_locked) > - mmap_read_unlock(current->mm); > - else > - vma_end_read(vma); > + vma_end_read(vma); > /* Try to copy straggler data. */ > if (!ret) > copylen = tcp_zc_handle_leftover(zc, sk, skb, &seq, copybuf_len, tss);