The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
called twice in each path currently.
This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
and sk_clone_lock().
Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
CC: Tariq Toukan <[email protected]>
CC: Boris Pismenny <[email protected]>
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Reviewed-by: Amit Shah <[email protected]>
---
net/core/sock.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/net/core/sock.c b/net/core/sock.c
index bbcd4b97eddd..5c665ee14159 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
cgroup_sk_alloc(&sk->sk_cgrp_data);
sock_update_classid(&sk->sk_cgrp_data);
sock_update_netprioidx(&sk->sk_cgrp_data);
- sk_tx_queue_clear(sk);
}
return sk;
@@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
*/
sk_refcnt_debug_inc(newsk);
sk_set_socket(newsk, NULL);
- sk_tx_queue_clear(newsk);
RCU_INIT_POINTER(newsk->sk_wq, NULL);
if (newsk->sk_prot->sockets_allocated)
--
2.17.2 (Apple Git-113)
On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> called twice in each path currently.
Are you sure ?
I do not clearly see the sk_tx_queue_clear() call from the cloning part.
Please elaborate.
In any case, this seems to be a candidate for net-next, this is not
fixing a bug,
this would be an optimization at most, and potentially adding a bug.
So if you resend this patch, you can mention the old commit in the changelog,
but do not add a dubious Fixes: tag
>
> This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> and sk_clone_lock().
>
> Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> CC: Tariq Toukan <[email protected]>
> CC: Boris Pismenny <[email protected]>
> Signed-off-by: Kuniyuki Iwashima <[email protected]>
> Reviewed-by: Amit Shah <[email protected]>
> ---
> net/core/sock.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index bbcd4b97eddd..5c665ee14159 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> cgroup_sk_alloc(&sk->sk_cgrp_data);
> sock_update_classid(&sk->sk_cgrp_data);
> sock_update_netprioidx(&sk->sk_cgrp_data);
> - sk_tx_queue_clear(sk);
> }
>
> return sk;
> @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> */
> sk_refcnt_debug_inc(newsk);
> sk_set_socket(newsk, NULL);
> - sk_tx_queue_clear(newsk);
> RCU_INIT_POINTER(newsk->sk_wq, NULL);
>
> if (newsk->sk_prot->sockets_allocated)
> --
> 2.17.2 (Apple Git-113)
>
On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> From: Eric Dumazet <[email protected]>
> Date: Wed, 27 Jan 2021 15:54:32 +0100
> > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > >
> > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > called twice in each path currently.
> >
> > Are you sure ?
> >
> > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> >
> > Please elaborate.
>
> If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> each function [2][3].
>
> In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> overwrite skc_tx_queue_mapping, and thus we can initialize it in
> sk_prot_alloc().
That is a lot of assumptions.
What guarantees do we have that skc_tx_queue_mapping will never be
moved out of this section ?
AFAIK it was there by accident, for cache locality reasons, that might
change in the future as we add more stuff in socket.
I feel this optimization is risky for future changes, for a code path
that is spending thousands of cycles anyway.
>
> [1] sk_prot_alloc
> https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
>
> [2] sk_alloc
> https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
>
> [3] sk_clone_lock
> https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
>
> [4] struct sock_common
> https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
>
>
> > In any case, this seems to be a candidate for net-next, this is not
> > fixing a bug,
> > this would be an optimization at most, and potentially adding a bug.
> >
> > So if you resend this patch, you can mention the old commit in the changelog,
> > but do not add a dubious Fixes: tag
>
> I see.
>
> I will remove the tag and resend this as a net-next candidate.
>
> Thank you,
> Kuniyuki
>
>
> > >
> > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > and sk_clone_lock().
> > >
> > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > CC: Tariq Toukan <[email protected]>
> > > CC: Boris Pismenny <[email protected]>
> > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > Reviewed-by: Amit Shah <[email protected]>
> > > ---
> > > net/core/sock.c | 2 --
> > > 1 file changed, 2 deletions(-)
> > >
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index bbcd4b97eddd..5c665ee14159 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > sock_update_classid(&sk->sk_cgrp_data);
> > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > - sk_tx_queue_clear(sk);
> > > }
> > >
> > > return sk;
> > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > */
> > > sk_refcnt_debug_inc(newsk);
> > > sk_set_socket(newsk, NULL);
> > > - sk_tx_queue_clear(newsk);
> > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > >
> > > if (newsk->sk_prot->sockets_allocated)
> > > --
> > > 2.17.2 (Apple Git-113)
> > >
From: Eric Dumazet <[email protected]>
Date: Wed, 27 Jan 2021 15:54:32 +0100
> On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> >
> > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > called twice in each path currently.
>
> Are you sure ?
>
> I do not clearly see the sk_tx_queue_clear() call from the cloning part.
>
> Please elaborate.
If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
If they finally return not NULL pointer, sk_tx_queue_clear() is called in
each function [2][3].
In the cloning part, sock_copy() is called after sk_prot_alloc(), but
skc_tx_queue_mapping is defined between skc_dontcopy_begin and
skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
overwrite skc_tx_queue_mapping, and thus we can initialize it in
sk_prot_alloc().
[1] sk_prot_alloc
https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
[2] sk_alloc
https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
[3] sk_clone_lock
https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
[4] struct sock_common
https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> In any case, this seems to be a candidate for net-next, this is not
> fixing a bug,
> this would be an optimization at most, and potentially adding a bug.
>
> So if you resend this patch, you can mention the old commit in the changelog,
> but do not add a dubious Fixes: tag
I see.
I will remove the tag and resend this as a net-next candidate.
Thank you,
Kuniyuki
> >
> > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > and sk_clone_lock().
> >
> > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > CC: Tariq Toukan <[email protected]>
> > CC: Boris Pismenny <[email protected]>
> > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > Reviewed-by: Amit Shah <[email protected]>
> > ---
> > net/core/sock.c | 2 --
> > 1 file changed, 2 deletions(-)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index bbcd4b97eddd..5c665ee14159 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > sock_update_classid(&sk->sk_cgrp_data);
> > sock_update_netprioidx(&sk->sk_cgrp_data);
> > - sk_tx_queue_clear(sk);
> > }
> >
> > return sk;
> > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > */
> > sk_refcnt_debug_inc(newsk);
> > sk_set_socket(newsk, NULL);
> > - sk_tx_queue_clear(newsk);
> > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> >
> > if (newsk->sk_prot->sockets_allocated)
> > --
> > 2.17.2 (Apple Git-113)
> >
From: Eric Dumazet <[email protected]>
Date: Wed, 27 Jan 2021 18:05:24 +0100
> On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
> >
> > From: Eric Dumazet <[email protected]>
> > Date: Wed, 27 Jan 2021 15:54:32 +0100
> > > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > >
> > > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > > called twice in each path currently.
> > >
> > > Are you sure ?
> > >
> > > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> > >
> > > Please elaborate.
> >
> > If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> > Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> > If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> > each function [2][3].
> >
> > In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> > skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> > skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> > overwrite skc_tx_queue_mapping, and thus we can initialize it in
> > sk_prot_alloc().
>
> That is a lot of assumptions.
>
> What guarantees do we have that skc_tx_queue_mapping will never be
> moved out of this section ?
> AFAIK it was there by accident, for cache locality reasons, that might
> change in the future as we add more stuff in socket.
>
> I feel this optimization is risky for future changes, for a code path
> that is spending thousands of cycles anyway.
If someone try to move skc_tx_queue_mapping out of the section, should
they take care about where it is used ?
But I agree that we should not write error-prone code.
Currently, sk_tx_queue_clear() is the only initialization code in
sk_prot_alloc(). So, does it make sense to remove sk_tx_queue_clear() in
sk_prot_alloc() so that it does only allocation and other fields are
initialized in each caller ?
> >
> > [1] sk_prot_alloc
> > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
> >
> > [2] sk_alloc
> > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
> >
> > [3] sk_clone_lock
> > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
> >
> > [4] struct sock_common
> > https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> >
> >
> > > In any case, this seems to be a candidate for net-next, this is not
> > > fixing a bug,
> > > this would be an optimization at most, and potentially adding a bug.
> > >
> > > So if you resend this patch, you can mention the old commit in the changelog,
> > > but do not add a dubious Fixes: tag
> >
> > I see.
> >
> > I will remove the tag and resend this as a net-next candidate.
> >
> > Thank you,
> > Kuniyuki
> >
> >
> > > >
> > > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > > and sk_clone_lock().
> > > >
> > > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > > CC: Tariq Toukan <[email protected]>
> > > > CC: Boris Pismenny <[email protected]>
> > > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > > Reviewed-by: Amit Shah <[email protected]>
> > > > ---
> > > > net/core/sock.c | 2 --
> > > > 1 file changed, 2 deletions(-)
> > > >
> > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > index bbcd4b97eddd..5c665ee14159 100644
> > > > --- a/net/core/sock.c
> > > > +++ b/net/core/sock.c
> > > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > > sock_update_classid(&sk->sk_cgrp_data);
> > > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > > - sk_tx_queue_clear(sk);
> > > > }
> > > >
> > > > return sk;
> > > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > > */
> > > > sk_refcnt_debug_inc(newsk);
> > > > sk_set_socket(newsk, NULL);
> > > > - sk_tx_queue_clear(newsk);
> > > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > > >
> > > > if (newsk->sk_prot->sockets_allocated)
> > > > --
> > > > 2.17.2 (Apple Git-113)
> > > >
On Wed, Jan 27, 2021 at 6:32 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> From: Eric Dumazet <[email protected]>
> Date: Wed, 27 Jan 2021 18:05:24 +0100
> > On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
> > >
> > > From: Eric Dumazet <[email protected]>
> > > Date: Wed, 27 Jan 2021 15:54:32 +0100
> > > > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > >
> > > > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > > > called twice in each path currently.
> > > >
> > > > Are you sure ?
> > > >
> > > > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> > > >
> > > > Please elaborate.
> > >
> > > If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> > > Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> > > If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> > > each function [2][3].
> > >
> > > In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> > > skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> > > skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> > > overwrite skc_tx_queue_mapping, and thus we can initialize it in
> > > sk_prot_alloc().
> >
> > That is a lot of assumptions.
> >
> > What guarantees do we have that skc_tx_queue_mapping will never be
> > moved out of this section ?
> > AFAIK it was there by accident, for cache locality reasons, that might
> > change in the future as we add more stuff in socket.
> >
> > I feel this optimization is risky for future changes, for a code path
> > that is spending thousands of cycles anyway.
>
> If someone try to move skc_tx_queue_mapping out of the section, should
> they take care about where it is used ?
Certainly not. You hide some knowledge, without a comment or some runtime check.
You can not ask us (maintainers) to remember thousands of tricks.
>
> But I agree that we should not write error-prone code.
>
> Currently, sk_tx_queue_clear() is the only initialization code in
> sk_prot_alloc(). So, does it make sense to remove sk_tx_queue_clear() in
> sk_prot_alloc() so that it does only allocation and other fields are
> initialized in each caller ?
>
>
> > >
> > > [1] sk_prot_alloc
> > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
> > >
> > > [2] sk_alloc
> > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
> > >
> > > [3] sk_clone_lock
> > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
> > >
> > > [4] struct sock_common
> > > https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> > >
> > >
> > > > In any case, this seems to be a candidate for net-next, this is not
> > > > fixing a bug,
> > > > this would be an optimization at most, and potentially adding a bug.
> > > >
> > > > So if you resend this patch, you can mention the old commit in the changelog,
> > > > but do not add a dubious Fixes: tag
> > >
> > > I see.
> > >
> > > I will remove the tag and resend this as a net-next candidate.
> > >
> > > Thank you,
> > > Kuniyuki
> > >
> > >
> > > > >
> > > > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > > > and sk_clone_lock().
> > > > >
> > > > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > > > CC: Tariq Toukan <[email protected]>
> > > > > CC: Boris Pismenny <[email protected]>
> > > > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > > > Reviewed-by: Amit Shah <[email protected]>
> > > > > ---
> > > > > net/core/sock.c | 2 --
> > > > > 1 file changed, 2 deletions(-)
> > > > >
> > > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > > index bbcd4b97eddd..5c665ee14159 100644
> > > > > --- a/net/core/sock.c
> > > > > +++ b/net/core/sock.c
> > > > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > > > sock_update_classid(&sk->sk_cgrp_data);
> > > > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > > > - sk_tx_queue_clear(sk);
> > > > > }
> > > > >
> > > > > return sk;
> > > > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > > > */
> > > > > sk_refcnt_debug_inc(newsk);
> > > > > sk_set_socket(newsk, NULL);
> > > > > - sk_tx_queue_clear(newsk);
> > > > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > > > >
> > > > > if (newsk->sk_prot->sockets_allocated)
> > > > > --
> > > > > 2.17.2 (Apple Git-113)
> > > > >
On Wed, Jan 27, 2021 at 6:56 PM Kuniyuki Iwashima <[email protected]> wrote:
>
> From: Eric Dumazet <[email protected]>
> Date: Wed, 27 Jan 2021 18:34:35 +0100
> > On Wed, Jan 27, 2021 at 6:32 PM Kuniyuki Iwashima <[email protected]> wrote:
> > >
> > > From: Eric Dumazet <[email protected]>
> > > Date: Wed, 27 Jan 2021 18:05:24 +0100
> > > > On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > >
> > > > > From: Eric Dumazet <[email protected]>
> > > > > Date: Wed, 27 Jan 2021 15:54:32 +0100
> > > > > > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > > > >
> > > > > > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > > > > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > > > > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > > > > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > > > > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > > > > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > > > > > called twice in each path currently.
> > > > > >
> > > > > > Are you sure ?
> > > > > >
> > > > > > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> > > > > >
> > > > > > Please elaborate.
> > > > >
> > > > > If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> > > > > Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> > > > > If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> > > > > each function [2][3].
> > > > >
> > > > > In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> > > > > skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> > > > > skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> > > > > overwrite skc_tx_queue_mapping, and thus we can initialize it in
> > > > > sk_prot_alloc().
> > > >
> > > > That is a lot of assumptions.
> > > >
> > > > What guarantees do we have that skc_tx_queue_mapping will never be
> > > > moved out of this section ?
> > > > AFAIK it was there by accident, for cache locality reasons, that might
> > > > change in the future as we add more stuff in socket.
> > > >
> > > > I feel this optimization is risky for future changes, for a code path
> > > > that is spending thousands of cycles anyway.
> > >
> > > If someone try to move skc_tx_queue_mapping out of the section, should
> > > they take care about where it is used ?
>
> I'm sorry if it might be misleading, I would like to mean someone/they is
> the author of a patch to move skc_tx_queue_mapping.
>
>
> > Certainly not. You hide some knowledge, without a comment or some runtime check.
>
> It was my bad, I should have written about sock_copy() in the changelog.
I think you also want to add some compile time check.
BUILD_BUG_ON( skc_tx_queue_mapping is in the no copy area)
Because maintainers do not remember changelogs in their mind.
>
>
> > You can not ask us (maintainers) to remember thousands of tricks.
>
> I'll keep this in mind.
>
>
> > >
> > > But I agree that we should not write error-prone code.
> > >
> > > Currently, sk_tx_queue_clear() is the only initialization code in
> > > sk_prot_alloc(). So, does it make sense to remove sk_tx_queue_clear() in
> > > sk_prot_alloc() so that it does only allocation and other fields are
> > > initialized in each caller ?
>
> Can I ask what you think about this ?
Yes, this would be fine.
>
>
> > > > >
> > > > > [1] sk_prot_alloc
> > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
> > > > >
> > > > > [2] sk_alloc
> > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
> > > > >
> > > > > [3] sk_clone_lock
> > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
> > > > >
> > > > > [4] struct sock_common
> > > > > https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> > > > >
> > > > >
> > > > > > In any case, this seems to be a candidate for net-next, this is not
> > > > > > fixing a bug,
> > > > > > this would be an optimization at most, and potentially adding a bug.
> > > > > >
> > > > > > So if you resend this patch, you can mention the old commit in the changelog,
> > > > > > but do not add a dubious Fixes: tag
> > > > >
> > > > > I see.
> > > > >
> > > > > I will remove the tag and resend this as a net-next candidate.
> > > > >
> > > > > Thank you,
> > > > > Kuniyuki
> > > > >
> > > > >
> > > > > > >
> > > > > > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > > > > > and sk_clone_lock().
> > > > > > >
> > > > > > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > > > > > CC: Tariq Toukan <[email protected]>
> > > > > > > CC: Boris Pismenny <[email protected]>
> > > > > > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > > > > > Reviewed-by: Amit Shah <[email protected]>
> > > > > > > ---
> > > > > > > net/core/sock.c | 2 --
> > > > > > > 1 file changed, 2 deletions(-)
> > > > > > >
> > > > > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > > > > index bbcd4b97eddd..5c665ee14159 100644
> > > > > > > --- a/net/core/sock.c
> > > > > > > +++ b/net/core/sock.c
> > > > > > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > > > > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > > > > > sock_update_classid(&sk->sk_cgrp_data);
> > > > > > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > > > > > - sk_tx_queue_clear(sk);
> > > > > > > }
> > > > > > >
> > > > > > > return sk;
> > > > > > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > > > > > */
> > > > > > > sk_refcnt_debug_inc(newsk);
> > > > > > > sk_set_socket(newsk, NULL);
> > > > > > > - sk_tx_queue_clear(newsk);
> > > > > > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > > > > > >
> > > > > > > if (newsk->sk_prot->sockets_allocated)
> > > > > > > --
> > > > > > > 2.17.2 (Apple Git-113)
> > > > > > >
From: Eric Dumazet <[email protected]>
Date: Wed, 27 Jan 2021 18:34:35 +0100
> On Wed, Jan 27, 2021 at 6:32 PM Kuniyuki Iwashima <[email protected]> wrote:
> >
> > From: Eric Dumazet <[email protected]>
> > Date: Wed, 27 Jan 2021 18:05:24 +0100
> > > On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > >
> > > > From: Eric Dumazet <[email protected]>
> > > > Date: Wed, 27 Jan 2021 15:54:32 +0100
> > > > > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > > >
> > > > > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > > > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > > > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > > > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > > > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > > > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > > > > called twice in each path currently.
> > > > >
> > > > > Are you sure ?
> > > > >
> > > > > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> > > > >
> > > > > Please elaborate.
> > > >
> > > > If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> > > > Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> > > > If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> > > > each function [2][3].
> > > >
> > > > In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> > > > skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> > > > skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> > > > overwrite skc_tx_queue_mapping, and thus we can initialize it in
> > > > sk_prot_alloc().
> > >
> > > That is a lot of assumptions.
> > >
> > > What guarantees do we have that skc_tx_queue_mapping will never be
> > > moved out of this section ?
> > > AFAIK it was there by accident, for cache locality reasons, that might
> > > change in the future as we add more stuff in socket.
> > >
> > > I feel this optimization is risky for future changes, for a code path
> > > that is spending thousands of cycles anyway.
> >
> > If someone try to move skc_tx_queue_mapping out of the section, should
> > they take care about where it is used ?
I'm sorry if it might be misleading, I would like to mean someone/they is
the author of a patch to move skc_tx_queue_mapping.
> Certainly not. You hide some knowledge, without a comment or some runtime check.
It was my bad, I should have written about sock_copy() in the changelog.
> You can not ask us (maintainers) to remember thousands of tricks.
I'll keep this in mind.
> >
> > But I agree that we should not write error-prone code.
> >
> > Currently, sk_tx_queue_clear() is the only initialization code in
> > sk_prot_alloc(). So, does it make sense to remove sk_tx_queue_clear() in
> > sk_prot_alloc() so that it does only allocation and other fields are
> > initialized in each caller ?
Can I ask what you think about this ?
> > > >
> > > > [1] sk_prot_alloc
> > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
> > > >
> > > > [2] sk_alloc
> > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
> > > >
> > > > [3] sk_clone_lock
> > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
> > > >
> > > > [4] struct sock_common
> > > > https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> > > >
> > > >
> > > > > In any case, this seems to be a candidate for net-next, this is not
> > > > > fixing a bug,
> > > > > this would be an optimization at most, and potentially adding a bug.
> > > > >
> > > > > So if you resend this patch, you can mention the old commit in the changelog,
> > > > > but do not add a dubious Fixes: tag
> > > >
> > > > I see.
> > > >
> > > > I will remove the tag and resend this as a net-next candidate.
> > > >
> > > > Thank you,
> > > > Kuniyuki
> > > >
> > > >
> > > > > >
> > > > > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > > > > and sk_clone_lock().
> > > > > >
> > > > > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > > > > CC: Tariq Toukan <[email protected]>
> > > > > > CC: Boris Pismenny <[email protected]>
> > > > > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > > > > Reviewed-by: Amit Shah <[email protected]>
> > > > > > ---
> > > > > > net/core/sock.c | 2 --
> > > > > > 1 file changed, 2 deletions(-)
> > > > > >
> > > > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > > > index bbcd4b97eddd..5c665ee14159 100644
> > > > > > --- a/net/core/sock.c
> > > > > > +++ b/net/core/sock.c
> > > > > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > > > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > > > > sock_update_classid(&sk->sk_cgrp_data);
> > > > > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > > > > - sk_tx_queue_clear(sk);
> > > > > > }
> > > > > >
> > > > > > return sk;
> > > > > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > > > > */
> > > > > > sk_refcnt_debug_inc(newsk);
> > > > > > sk_set_socket(newsk, NULL);
> > > > > > - sk_tx_queue_clear(newsk);
> > > > > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > > > > >
> > > > > > if (newsk->sk_prot->sockets_allocated)
> > > > > > --
> > > > > > 2.17.2 (Apple Git-113)
> > > > > >
From: Eric Dumazet <[email protected]>
Date: Wed, 27 Jan 2021 19:07:51 +0100
> On Wed, Jan 27, 2021 at 6:56 PM Kuniyuki Iwashima <[email protected]> wrote:
> >
> > From: Eric Dumazet <[email protected]>
> > Date: Wed, 27 Jan 2021 18:34:35 +0100
> > > On Wed, Jan 27, 2021 at 6:32 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > >
> > > > From: Eric Dumazet <[email protected]>
> > > > Date: Wed, 27 Jan 2021 18:05:24 +0100
> > > > > On Wed, Jan 27, 2021 at 5:52 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > > >
> > > > > > From: Eric Dumazet <[email protected]>
> > > > > > Date: Wed, 27 Jan 2021 15:54:32 +0100
> > > > > > > On Wed, Jan 27, 2021 at 1:50 PM Kuniyuki Iwashima <[email protected]> wrote:
> > > > > > > >
> > > > > > > > The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
> > > > > > > > sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
> > > > > > > > it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
> > > > > > > > the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). However,
> > > > > > > > the original commit had already put sk_tx_queue_clear() in sk_prot_alloc():
> > > > > > > > the callee of sk_alloc() and sk_clone_lock(). Thus sk_tx_queue_clear() is
> > > > > > > > called twice in each path currently.
> > > > > > >
> > > > > > > Are you sure ?
> > > > > > >
> > > > > > > I do not clearly see the sk_tx_queue_clear() call from the cloning part.
> > > > > > >
> > > > > > > Please elaborate.
> > > > > >
> > > > > > If sk is not NULL in sk_prot_alloc(), sk_tx_queue_clear() is called [1].
> > > > > > Also the callers of sk_prot_alloc() are only sk_alloc() and sk_clone_lock().
> > > > > > If they finally return not NULL pointer, sk_tx_queue_clear() is called in
> > > > > > each function [2][3].
> > > > > >
> > > > > > In the cloning part, sock_copy() is called after sk_prot_alloc(), but
> > > > > > skc_tx_queue_mapping is defined between skc_dontcopy_begin and
> > > > > > skc_dontcopy_end in struct sock_common [4]. So, sock_copy() does not
> > > > > > overwrite skc_tx_queue_mapping, and thus we can initialize it in
> > > > > > sk_prot_alloc().
> > > > >
> > > > > That is a lot of assumptions.
> > > > >
> > > > > What guarantees do we have that skc_tx_queue_mapping will never be
> > > > > moved out of this section ?
> > > > > AFAIK it was there by accident, for cache locality reasons, that might
> > > > > change in the future as we add more stuff in socket.
> > > > >
> > > > > I feel this optimization is risky for future changes, for a code path
> > > > > that is spending thousands of cycles anyway.
> > > >
> > > > If someone try to move skc_tx_queue_mapping out of the section, should
> > > > they take care about where it is used ?
> >
> > I'm sorry if it might be misleading, I would like to mean someone/they is
> > the author of a patch to move skc_tx_queue_mapping.
> >
> >
> > > Certainly not. You hide some knowledge, without a comment or some runtime check.
> >
> > It was my bad, I should have written about sock_copy() in the changelog.
>
> I think you also want to add some compile time check.
>
> BUILD_BUG_ON( skc_tx_queue_mapping is in the no copy area)
>
> Because maintainers do not remember changelogs in their mind.
I understand.
The proper place to add BUILD_BUG_ON() is sock_copy() or sk_clone_lock() ?
> >
> >
> > > You can not ask us (maintainers) to remember thousands of tricks.
> >
> > I'll keep this in mind.
> >
> >
> > > >
> > > > But I agree that we should not write error-prone code.
> > > >
> > > > Currently, sk_tx_queue_clear() is the only initialization code in
> > > > sk_prot_alloc(). So, does it make sense to remove sk_tx_queue_clear() in
> > > > sk_prot_alloc() so that it does only allocation and other fields are
> > > > initialized in each caller ?
> >
> > Can I ask what you think about this ?
>
> Yes, this would be fine.
Thank you, I will remove the sk_tx_queue_clear() in sk_prot_alloc().
> >
> > > > > >
> > > > > > [1] sk_prot_alloc
> > > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1693
> > > > > >
> > > > > > [2] sk_alloc
> > > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1762
> > > > > >
> > > > > > [3] sk_clone_lock
> > > > > > https://github.com/torvalds/linux/blob/master/net/core/sock.c#L1986
> > > > > >
> > > > > > [4] struct sock_common
> > > > > > https://github.com/torvalds/linux/blob/master/include/net/sock.h#L218-L240
> > > > > >
> > > > > >
> > > > > > > In any case, this seems to be a candidate for net-next, this is not
> > > > > > > fixing a bug,
> > > > > > > this would be an optimization at most, and potentially adding a bug.
> > > > > > >
> > > > > > > So if you resend this patch, you can mention the old commit in the changelog,
> > > > > > > but do not add a dubious Fixes: tag
> > > > > >
> > > > > > I see.
> > > > > >
> > > > > > I will remove the tag and resend this as a net-next candidate.
> > > > > >
> > > > > > Thank you,
> > > > > > Kuniyuki
> > > > > >
> > > > > >
> > > > > > > >
> > > > > > > > This patch removes the redundant calls of sk_tx_queue_clear() in sk_alloc()
> > > > > > > > and sk_clone_lock().
> > > > > > > >
> > > > > > > > Fixes: 41b14fb8724d ("net: Do not clear the sock TX queue in sk_set_socket()")
> > > > > > > > CC: Tariq Toukan <[email protected]>
> > > > > > > > CC: Boris Pismenny <[email protected]>
> > > > > > > > Signed-off-by: Kuniyuki Iwashima <[email protected]>
> > > > > > > > Reviewed-by: Amit Shah <[email protected]>
> > > > > > > > ---
> > > > > > > > net/core/sock.c | 2 --
> > > > > > > > 1 file changed, 2 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > > > > > index bbcd4b97eddd..5c665ee14159 100644
> > > > > > > > --- a/net/core/sock.c
> > > > > > > > +++ b/net/core/sock.c
> > > > > > > > @@ -1759,7 +1759,6 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
> > > > > > > > cgroup_sk_alloc(&sk->sk_cgrp_data);
> > > > > > > > sock_update_classid(&sk->sk_cgrp_data);
> > > > > > > > sock_update_netprioidx(&sk->sk_cgrp_data);
> > > > > > > > - sk_tx_queue_clear(sk);
> > > > > > > > }
> > > > > > > >
> > > > > > > > return sk;
> > > > > > > > @@ -1983,7 +1982,6 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
> > > > > > > > */
> > > > > > > > sk_refcnt_debug_inc(newsk);
> > > > > > > > sk_set_socket(newsk, NULL);
> > > > > > > > - sk_tx_queue_clear(newsk);
> > > > > > > > RCU_INIT_POINTER(newsk->sk_wq, NULL);
> > > > > > > >
> > > > > > > > if (newsk->sk_prot->sockets_allocated)
> > > > > > > > --
> > > > > > > > 2.17.2 (Apple Git-113)
> > > > > > > >