Re: [PATCH v2 5/5] tcp: Remove mmap_lock fallback path
From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-06-11 20:45:00
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linux-mm, lkml
On Wed, Jun 10, 2026 at 4:04 PM Dave Hansen [off-list ref] wrote:
From: Dave Hansen <dave.hansen@linux.intel.com> Previously, the per-VMA locking could fail in the face of writers which necessitates a fallback to mmap_lock. The new lock_vma_under_rcu_wait() will wait for writers instead of failing. Use the new helper. Wait for writers. Remove the fallback to mmap_lock. This really is a nice cleanup. It removes the need to pass the lock state back and forth to find_tcp_vma().
LGTM. As in the previous patch, you already have my Reviewed-by.
quoted hunk ↗ jump to hunk
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Lorenzo Stoakes <ljs@kernel.org> Reviewed-by: Suren Baghdasaryan <surenb@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: "Liam R. Howlett" <redacted> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: linux-mm@kvack.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Arve Hjønnevåg <arve@android.com> Cc: Todd Kjos <tkjos@android.com> Cc: Christian Brauner <christian@brauner.io> Cc: Carlos Llamas <cmllamas@google.com> Cc: Alice Ryhl <aliceryhl@google.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: David Ahern <dsahern@kernel.org> Cc: netdev@vger.kernel.org --- b/net/ipv4/tcp.c | 31 +++++++++---------------------- 1 file changed, 9 insertions(+), 22 deletions(-) diff -puN net/ipv4/tcp.c~ipv4-tcp-vma-waiter net/ipv4/tcp.c--- a/net/ipv4/tcp.c~ipv4-tcp-vma-waiter 2026-06-10 15:57:56.972472379 -0700 +++ b/net/ipv4/tcp.c 2026-06-10 15:57:56.976472521 -0700@@ -2171,27 +2171,18 @@ static void tcp_zc_finalize_rx_tstamp(st } 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; }@@ -2212,7 +2203,6 @@ static int tcp_zerocopy_receive(struct s u32 seq = tp->copied_seq; u32 total_bytes_to_map; int inq = tcp_inq(sk); - bool mmap_locked; int ret; zc->copybuf_len = 0;@@ -2237,7 +2227,7 @@ static int tcp_zerocopy_receive(struct s return 0; } - vma = find_tcp_vma(current->mm, address, &mmap_locked); + vma = find_tcp_vma(current->mm, address); if (!vma) return -EINVAL;@@ -2319,10 +2309,7 @@ static int tcp_zerocopy_receive(struct s 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);_