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 4BD9E37BE72; Fri, 12 Jun 2026 18:13:34 +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=1781288015; cv=none; b=HhtoGsyMshRuaJF6H1mRKHLh72TNIJN0j0ZAXQSR7hpwfRKhcwFtsLt2eX0q17PoXqextZOhZP+BesPa5f2ePBaLj0PNmDmY089qtb0sco3etO/uCfprk0UqNPn5FL1xJLbdGyoh43H7Ydq9SZ3taMd3Qv15xO6dOELZft0H/IM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781288015; c=relaxed/simple; bh=+6z8gqF/pdow2lk8DKYm++IRzUTSm8oNDeHTGnJd4Ag=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XBVXVWMGoyyfQ6UJO7Qf4xTK58RnOuUMT0C/JxV7RY3xPg0GGNjS3BJuRe7VVBwPApOk0l+D9Z5Tkzi20P3Vdkr/De7hqKQtXT/PjDJ9bKfZk+v9oPhkKkWSBaHzPBLATpkrGfMoQPbKjmUT4SRVzqOIR1rcmjIvmsHdGiGK5A8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Knp+OTXm; 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="Knp+OTXm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCFFA1F000E9; Fri, 12 Jun 2026 18:13:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781288014; bh=ZwYCwWeTmmit2nkq41jaq0H1yOqgsyEenFLXnjwhYwo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Knp+OTXmxpJsuycvT2MDrvTJmS28MPVDNDq2Bi4qIf3DU7ohoSsXN4dpusHwxfTKk A2qbx9SD1c1/Glxr/qsTRZn1ErINL+Fk3zpKOHHj+Gw/b3PU25AehhfCh0uMB9qCxU AfUd3l8TypCoN80kz3uiWawkN6ipZh3SVs0qnTqrZtfiwXPcdunyjYpnegriqgQVCO CPBwuRhKcR7iKFf8LhgpdaAla0LT8VQMNoRoMsKF326iRZ6rGf04YG1gOHOgCRhcs2 WlJ8WPNJkfsfmm++KPhSNAN631Z/+vzqcwhDjubuQrg9o5lzzP0eH3Ml142HAMpR0e seBbgFVn7ZviA== Message-ID: <5e024bf5-2d0e-4249-9561-f32081ec29bc@kernel.org> Date: Fri, 12 Jun 2026 20:13:29 +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 v2 5/5] tcp: Remove mmap_lock fallback path Content-Language: en-US To: Dave Hansen , linux-kernel@vger.kernel.org Cc: Alice Ryhl , Andrew Morton , =?UTF-8?B?QXJ2ZSBIasO4bm5ldsOl?= =?UTF-8?Q?g?= , Carlos Llamas , Christian Brauner , David Ahern , "David S. Miller" , Greg Kroah-Hartman , "Liam R. Howlett" , linux-mm@kvack.org, Lorenzo Stoakes , netdev@vger.kernel.org, Shakeel Butt , Suren Baghdasaryan , Todd Kjos References: <20260610230409.A44D29FA@davehans-spike.ostc.intel.com> <20260610230419.F746395F@davehans-spike.ostc.intel.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260610230419.F746395F@davehans-spike.ostc.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 6/11/26 01:04, Dave Hansen 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 > lock_vma_under_rcu_wait() will wait for writers instead of failing. vma_start_read_unlocked() > > Use the new helper. Wait for writers. Remove the fallback to mmap_lock. > > This really is a nice cleanup. [obama_medal_meme.jpg] ;) But yeah, it is! > 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 > Reviewed-by: Suren Baghdasaryan Acked-by: Vlastimil Babka (SUSE) > 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 > --- > > 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); > _