* [PATCH net] net: let skb_orphan_partial wake-up waiters.
@ 2021-03-30 14:24 Paolo Abeni
2021-03-30 14:39 ` Eric Dumazet
0 siblings, 1 reply; 6+ messages in thread
From: Paolo Abeni @ 2021-03-30 14:24 UTC (permalink / raw)
To: netdev; +Cc: Eric Dumazet
Currently the mentioned helper can end-up freeing the socket wmem
without waking-up any processes waiting for more write memory.
If the partially orphaned skb is attached to an UDP (or raw) socket,
the lack of wake-up can hang the user-space.
Address the issue invoking the write_space callback after
releasing the memory, if the old skb destructor requires that.
Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
net/core/sock.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/net/core/sock.c b/net/core/sock.c
index 0ed98f20448a2..7a38332d748e7 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2137,6 +2137,8 @@ void skb_orphan_partial(struct sk_buff *skb)
if (refcount_inc_not_zero(&sk->sk_refcnt)) {
WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
+ if (skb->destructor == sock_wfree)
+ sk->sk_write_space(sk);
skb->destructor = sock_efree;
}
} else {
--
2.26.2
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH net] net: let skb_orphan_partial wake-up waiters.
2021-03-30 14:24 [PATCH net] net: let skb_orphan_partial wake-up waiters Paolo Abeni
@ 2021-03-30 14:39 ` Eric Dumazet
2021-03-30 14:40 ` Eric Dumazet
0 siblings, 1 reply; 6+ messages in thread
From: Eric Dumazet @ 2021-03-30 14:39 UTC (permalink / raw)
To: Paolo Abeni; +Cc: netdev
On Tue, Mar 30, 2021 at 4:25 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> Currently the mentioned helper can end-up freeing the socket wmem
> without waking-up any processes waiting for more write memory.
>
> If the partially orphaned skb is attached to an UDP (or raw) socket,
> the lack of wake-up can hang the user-space.
>
> Address the issue invoking the write_space callback after
> releasing the memory, if the old skb destructor requires that.
>
> Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> net/core/sock.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 0ed98f20448a2..7a38332d748e7 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2137,6 +2137,8 @@ void skb_orphan_partial(struct sk_buff *skb)
>
> if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
> + if (skb->destructor == sock_wfree)
> + sk->sk_write_space(sk);
Interesting.
Why TCP is not a problem here ?
I would rather replace WARN_ON(refcount_sub_and_test(skb->truesize,
&sk->sk_wmem_alloc)) by :
skb_orphan(skb);
This will get rid of this suspect WARN_ON() at the same time ?
> skb->destructor = sock_efree;
> }
> } else {
> --
> 2.26.2
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net] net: let skb_orphan_partial wake-up waiters.
2021-03-30 14:39 ` Eric Dumazet
@ 2021-03-30 14:40 ` Eric Dumazet
2021-03-30 15:18 ` Paolo Abeni
0 siblings, 1 reply; 6+ messages in thread
From: Eric Dumazet @ 2021-03-30 14:40 UTC (permalink / raw)
To: Paolo Abeni; +Cc: netdev
On Tue, Mar 30, 2021 at 4:39 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Tue, Mar 30, 2021 at 4:25 PM Paolo Abeni <pabeni@redhat.com> wrote:
> >
> > Currently the mentioned helper can end-up freeing the socket wmem
> > without waking-up any processes waiting for more write memory.
> >
> > If the partially orphaned skb is attached to an UDP (or raw) socket,
> > the lack of wake-up can hang the user-space.
> >
> > Address the issue invoking the write_space callback after
> > releasing the memory, if the old skb destructor requires that.
> >
> > Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
> > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > ---
> > net/core/sock.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 0ed98f20448a2..7a38332d748e7 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -2137,6 +2137,8 @@ void skb_orphan_partial(struct sk_buff *skb)
> >
> > if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> > WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
> > + if (skb->destructor == sock_wfree)
> > + sk->sk_write_space(sk);
>
> Interesting.
>
> Why TCP is not a problem here ?
>
> I would rather replace WARN_ON(refcount_sub_and_test(skb->truesize,
> &sk->sk_wmem_alloc)) by :
> skb_orphan(skb);
And of course re-add
skb->sk = sk;
>
> This will get rid of this suspect WARN_ON() at the same time ?
>
> > skb->destructor = sock_efree;
> > }
> > } else {
> > --
> > 2.26.2
> >
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net] net: let skb_orphan_partial wake-up waiters.
2021-03-30 14:40 ` Eric Dumazet
@ 2021-03-30 15:18 ` Paolo Abeni
2021-03-30 15:29 ` Eric Dumazet
2021-03-30 15:32 ` Eric Dumazet
0 siblings, 2 replies; 6+ messages in thread
From: Paolo Abeni @ 2021-03-30 15:18 UTC (permalink / raw)
To: Eric Dumazet; +Cc: netdev
On Tue, 2021-03-30 at 16:40 +0200, Eric Dumazet wrote:
> On Tue, Mar 30, 2021 at 4:39 PM Eric Dumazet <edumazet@google.com> wrote:
> > On Tue, Mar 30, 2021 at 4:25 PM Paolo Abeni <pabeni@redhat.com> wrote:
> > > Currently the mentioned helper can end-up freeing the socket wmem
> > > without waking-up any processes waiting for more write memory.
> > >
> > > If the partially orphaned skb is attached to an UDP (or raw) socket,
> > > the lack of wake-up can hang the user-space.
> > >
> > > Address the issue invoking the write_space callback after
> > > releasing the memory, if the old skb destructor requires that.
> > >
> > > Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
> > > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > > ---
> > > net/core/sock.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index 0ed98f20448a2..7a38332d748e7 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -2137,6 +2137,8 @@ void skb_orphan_partial(struct sk_buff *skb)
> > >
> > > if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> > > WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
> > > + if (skb->destructor == sock_wfree)
> > > + sk->sk_write_space(sk);
> >
> > Interesting.
> >
> > Why TCP is not a problem here ?
AFAICS, tcp_wfree() does not call sk->sk_write_space(). Processes
waiting for wmem are woken by ack processing.
> > I would rather replace WARN_ON(refcount_sub_and_test(skb->truesize,
> > &sk->sk_wmem_alloc)) by :
> > skb_orphan(skb);
>
> And of course re-add
> skb->sk = sk;
Double checking to be sure. The patched slice of skb_orphan_partial()
will then look like:
if (can_skb_orphan_partial(skb)) {
struct sock *sk = skb->sk;
if (refcount_inc_not_zero(&sk->sk_refcnt)) {
skb_orphan(skb);
skb->sk = sk;
skb->destructor = sock_efree;
}
} // ...
Am I correct?
Thanks!
Paolo
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net] net: let skb_orphan_partial wake-up waiters.
2021-03-30 15:18 ` Paolo Abeni
@ 2021-03-30 15:29 ` Eric Dumazet
2021-03-30 15:32 ` Eric Dumazet
1 sibling, 0 replies; 6+ messages in thread
From: Eric Dumazet @ 2021-03-30 15:29 UTC (permalink / raw)
To: Paolo Abeni; +Cc: netdev
On Tue, Mar 30, 2021 at 5:18 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Tue, 2021-03-30 at 16:40 +0200, Eric Dumazet wrote:
> > On Tue, Mar 30, 2021 at 4:39 PM Eric Dumazet <edumazet@google.com> wrote:
> > > On Tue, Mar 30, 2021 at 4:25 PM Paolo Abeni <pabeni@redhat.com> wrote:
> > > > Currently the mentioned helper can end-up freeing the socket wmem
> > > > without waking-up any processes waiting for more write memory.
> > > >
> > > > If the partially orphaned skb is attached to an UDP (or raw) socket,
> > > > the lack of wake-up can hang the user-space.
> > > >
> > > > Address the issue invoking the write_space callback after
> > > > releasing the memory, if the old skb destructor requires that.
> > > >
> > > > Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
> > > > Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> > > > ---
> > > > net/core/sock.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > index 0ed98f20448a2..7a38332d748e7 100644
> > > > --- a/net/core/sock.c
> > > > +++ b/net/core/sock.c
> > > > @@ -2137,6 +2137,8 @@ void skb_orphan_partial(struct sk_buff *skb)
> > > >
> > > > if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> > > > WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
> > > > + if (skb->destructor == sock_wfree)
> > > > + sk->sk_write_space(sk);
> > >
> > > Interesting.
> > >
> > > Why TCP is not a problem here ?
>
> AFAICS, tcp_wfree() does not call sk->sk_write_space(). Processes
> waiting for wmem are woken by ack processing.
>
> > > I would rather replace WARN_ON(refcount_sub_and_test(skb->truesize,
> > > &sk->sk_wmem_alloc)) by :
> > > skb_orphan(skb);
> >
> > And of course re-add
> > skb->sk = sk;
>
> Double checking to be sure. The patched slice of skb_orphan_partial()
> will then look like:
>
> if (can_skb_orphan_partial(skb)) {
> struct sock *sk = skb->sk;
>
> if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> skb_orphan(skb);
> skb->sk = sk;
> skb->destructor = sock_efree;
> }
> } // ...
>
> Am I correct?
>
Yes.
We also could add a helper for the whole construct, since many other
paths do almost the same.
(They might use sock_hold(), but it seems safe to use the
refcount_inc_not_zero())
Or they omit the skb_orphan() (see can_skb_set_owner), which seems also risky.
static inline void skb_set_owner_sk_safe(sk, skb)
{
if (sk && refcount_inc_not_zero(&sk->sk_refcnt)) {
skb_orphan(skb);
skb->destructor = sock_efree;
skb->sk = sk;
}
}
> Thanks!
>
> Paolo
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net] net: let skb_orphan_partial wake-up waiters.
2021-03-30 15:18 ` Paolo Abeni
2021-03-30 15:29 ` Eric Dumazet
@ 2021-03-30 15:32 ` Eric Dumazet
1 sibling, 0 replies; 6+ messages in thread
From: Eric Dumazet @ 2021-03-30 15:32 UTC (permalink / raw)
To: Paolo Abeni; +Cc: netdev
On Tue, Mar 30, 2021 at 5:18 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Tue, 2021-03-30 at 16:40 +0200, Eric Dumazet wrote:
> > >
> > > Why TCP is not a problem here ?
>
> AFAICS, tcp_wfree() does not call sk->sk_write_space(). Processes
> waiting for wmem are woken by ack processing.
My concern was TCP Small Queue. If we do not call tcp_wfree() we might miss
an opportunity to queue more packets (and thus fallback to RTO or
incoming ACK is we are lucky)
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-03-30 15:33 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2021-03-30 14:24 [PATCH net] net: let skb_orphan_partial wake-up waiters Paolo Abeni
2021-03-30 14:39 ` Eric Dumazet
2021-03-30 14:40 ` Eric Dumazet
2021-03-30 15:18 ` Paolo Abeni
2021-03-30 15:29 ` Eric Dumazet
2021-03-30 15:32 ` Eric Dumazet
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