Re: [PATCH] net: fix race in the receive/select

Oleg Nesterov
2009-06-25T15:39:22Z

Can't really comment this patch, except this all looks reasonable to me.
Add more CCs.

On 06/25, Jiri Olsa wrote:
>
> Adding memory barrier to the __pollwait function paired with
> receive callbacks. The smp_mb__after_lock define is added,
> since {read|write|spin}_lock() on x86 are full memory barriers.
>
> The race fires, when following code paths meet, and the tp->rcv_nxt and
> __add_wait_queue updates stay in CPU caches.
>
>
> CPU1 CPU2
>
> sys_select receive packet
> ... ...
> __add_wait_queue update tp->rcv_nxt
> ... ...
> tp->rcv_nxt check sock_def_readable
> ... {
> schedule ...
> if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> wake_up_interruptible(sk->sk_sleep)
> ...
> }
>
> If there was no cache the code would work ok, since the wait_queue and
> rcv_nxt are opposit to each other.
>
> Meaning that once tp->rcv_nxt is updated by CPU2, the CPU1 either already
> passed the tp->rcv_nxt check and sleeps, or will get the new value for
> tp->rcv_nxt and will return with new data mask.
> In both cases the process (CPU1) is being added to the wait queue, so the
> waitqueue_active (CPU2) call cannot miss and will wake up CPU1.
>
> The bad case is when the __add_wait_queue changes done by CPU1 stay in its
> cache, and so does the tp->rcv_nxt update on CPU2 side. The CPU1 will then
> endup calling schedule and sleep forever if there are no more data on the
> socket.
>
> wbr,
> jirka
>
>
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
>
> ---
> arch/x86/include/asm/spinlock.h | 3 +++
> fs/select.c | 4 ++++
> include/linux/spinlock.h | 5 +++++
> include/net/sock.h | 18 ++++++++++++++++++
> net/atm/common.c | 4 ++--
> net/core/sock.c | 8 ++++----
> net/dccp/output.c | 2 +-
> net/iucv/af_iucv.c | 2 +-
> net/rxrpc/af_rxrpc.c | 2 +-
> net/unix/af_unix.c | 2 +-
> 10 files changed, 40 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
> index b7e5db8..39ecc5f 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw)
> #define _raw_read_relax(lock) cpu_relax()
> #define _raw_write_relax(lock) cpu_relax()
>
> +/* The {read|write|spin}_lock() on x86 are full memory barriers. */
> +#define smp_mb__after_lock() do { } while (0)
> +
> #endif /* _ASM_X86_SPINLOCK_H */
> diff --git a/fs/select.c b/fs/select.c
> index d870237..c4bd5f0 100644
> --- a/fs/select.c
> +++ b/fs/select.c
> @@ -219,6 +219,10 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
> init_waitqueue_func_entry(&entry->wait, pollwake);
> entry->wait.private = pwq;
> add_wait_queue(wait_address, &entry->wait);
> +
> + /* This memory barrier is paired with the smp_mb__after_lock
> + * in the sk_has_sleeper. */
> + smp_mb();
> }
>
> int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
> diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h
> index 252b245..ae053bd 100644
> --- a/include/linux/spinlock.h
> +++ b/include/linux/spinlock.h
> @@ -132,6 +132,11 @@ do { \
> #endif /*__raw_spin_is_contended*/
> #endif
>
> +/* The lock does not imply full memory barrier. */
> +#ifndef smp_mb__after_lock
> +#define smp_mb__after_lock() smp_mb()
> +#endif
> +
> /**
> * spin_unlock_wait - wait until the spinlock gets unlocked
> * @lock: the spinlock in question.
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 352f06b..7fbb143 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1241,6 +1241,24 @@ static inline int sk_has_allocations(const struct sock *sk)
> return sk_wmem_alloc_get(sk) || sk_rmem_alloc_get(sk);
> }
>
> +/**
> + * sk_has_sleeper - check if there are any waiting processes
> + * @sk: socket
> + *
> + * Returns true if socket has waiting processes
> + */
> +static inline int sk_has_sleeper(struct sock *sk)
> +{
> + /*
> + * We need to be sure we are in sync with the
> + * add_wait_queue modifications to the wait queue.
> + *
> + * This memory barrier is paired in the __pollwait.
> + */
> + smp_mb__after_lock();
> + return sk->sk_sleep && waitqueue_active(sk->sk_sleep);
> +}
> +
> /*
> * Queue a received datagram if it will fit. Stream and sequenced
> * protocols can't normally use this as they need to fit buffers in
> diff --git a/net/atm/common.c b/net/atm/common.c
> index c1c9793..67a8642 100644
> --- a/net/atm/common.c
> +++ b/net/atm/common.c
> @@ -92,7 +92,7 @@ static void vcc_sock_destruct(struct sock *sk)
> static void vcc_def_wakeup(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up(sk->sk_sleep);
> read_unlock(&sk->sk_callback_lock);
> }
> @@ -110,7 +110,7 @@ static void vcc_write_space(struct sock *sk)
> read_lock(&sk->sk_callback_lock);
>
> if (vcc_writable(sk)) {
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible(sk->sk_sleep);
>
> sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index b0ba569..6354863 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1715,7 +1715,7 @@ EXPORT_SYMBOL(sock_no_sendpage);
> static void sock_def_wakeup(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_all(sk->sk_sleep);
> read_unlock(&sk->sk_callback_lock);
> }
> @@ -1723,7 +1723,7 @@ static void sock_def_wakeup(struct sock *sk)
> static void sock_def_error_report(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_poll(sk->sk_sleep, POLLERR);
> sk_wake_async(sk, SOCK_WAKE_IO, POLL_ERR);
> read_unlock(&sk->sk_callback_lock);
> @@ -1732,7 +1732,7 @@ static void sock_def_error_report(struct sock *sk)
> static void sock_def_readable(struct sock *sk, int len)
> {
> read_lock(&sk->sk_callback_lock);
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_sync_poll(sk->sk_sleep, POLLIN |
> POLLRDNORM | POLLRDBAND);
> sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
> @@ -1747,7 +1747,7 @@ static void sock_def_write_space(struct sock *sk)
> * progress. --DaveM
> */
> if ((atomic_read(&sk->sk_wmem_alloc) << 1) <= sk->sk_sndbuf) {
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_sync_poll(sk->sk_sleep, POLLOUT |
> POLLWRNORM | POLLWRBAND);
>
> diff --git a/net/dccp/output.c b/net/dccp/output.c
> index c0e88c1..c96119f 100644
> --- a/net/dccp/output.c
> +++ b/net/dccp/output.c
> @@ -196,7 +196,7 @@ void dccp_write_space(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
>
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible(sk->sk_sleep);
> /* Should agree with poll, otherwise some programs break */
> if (sock_writeable(sk))
> diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
> index 6be5f92..ba0149d 100644
> --- a/net/iucv/af_iucv.c
> +++ b/net/iucv/af_iucv.c
> @@ -306,7 +306,7 @@ static inline int iucv_below_msglim(struct sock *sk)
> static void iucv_sock_wake_msglim(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_all(sk->sk_sleep);
> sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
> read_unlock(&sk->sk_callback_lock);
> diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
> index eac5e7b..60e0e38 100644
> --- a/net/rxrpc/af_rxrpc.c
> +++ b/net/rxrpc/af_rxrpc.c
> @@ -63,7 +63,7 @@ static void rxrpc_write_space(struct sock *sk)
> _enter("%p", sk);
> read_lock(&sk->sk_callback_lock);
> if (rxrpc_writable(sk)) {
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible(sk->sk_sleep);
> sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
> }
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 36d4e44..143143a 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -315,7 +315,7 @@ static void unix_write_space(struct sock *sk)
> {
> read_lock(&sk->sk_callback_lock);
> if (unix_writable(sk)) {
> - if (sk->sk_sleep && waitqueue_active(sk->sk_sleep))
> + if (sk_has_sleeper(sk))
> wake_up_interruptible_sync(sk->sk_sleep);
> sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
> }