linux-toradex.git/net/core/stream.c, branch v4.3-rc6

tcp: set SOCK_NOSPACE under memory pressure

2015-05-09T21:38:36+00:00

Under tcp memory pressure, calling epoll_wait() in edge triggered
mode after -EAGAIN, can result in an indefinite hang in epoll_wait(),
even when there is sufficient memory available to continue making
progress. The problem is that when __sk_mem_schedule() returns 0
under memory pressure, we do not set the SOCK_NOSPACE flag in the
tcp write paths (tcp_sendmsg() or do_tcp_sendpages()). Then, since
SOCK_NOSPACE is used to trigger wakeups when incoming acks create
sufficient new space in the write queue, all outstanding packets
are acked, but we never wake up with the the EPOLLOUT that we are
expecting from epoll_wait().

This issue is currently limited to epoll() when used in edge trigger
mode, since 'tcp_poll()', does in fact currently set SOCK_NOSPACE.
This is sufficient for poll()/select() and epoll() in level trigger
mode. However, in edge trigger mode, epoll() is relying on the write
path to set SOCK_NOSPACE. EPOLL(7) says that in edge-trigger mode we
can only call epoll_wait() after read/write return -EAGAIN. Thus, in
the case of the socket write, we are relying on the fact that
tcp_sendmsg()/network write paths are going to issue a wakeup for
us at some point in the future when we get -EAGAIN.

Normally, epoll() edge trigger works fine when we've exceeded the
sk->sndbuf because in that case we do set SOCK_NOSPACE. However, when
we return -EAGAIN from the write path b/c we are over the tcp memory
limits and not b/c we are over the sndbuf, we are never going to get
another wakeup.

I can reproduce this issue, using SO_SNDBUF, since __sk_mem_schedule()
will return 0, or failure more readily with SO_SNDBUF:

1) create socket and set SO_SNDBUF to N
2) add socket as edge trigger
3) write to socket and block in epoll on -EAGAIN
4) cause tcp mem pressure via: echo "" > net.ipv4.tcp_mem

The fix here is simply to set SOCK_NOSPACE in sk_stream_wait_memory()
when the socket is non-blocking. Note that SOCK_NOSPACE, in addition
to waking up outstanding waiters is also used to expand the size of
the sk->sndbuf. However, we will not expand it by setting it in this
case because tcp_should_expand_sndbuf(), ensures that no expansion
occurs when we are under tcp memory pressure.

Note that we could still hang if sk->sk_wmem_queue is 0, when we get
the -EAGAIN. In this case the SOCK_NOSPACE bit will not help, since we
are waiting for and event that will never happen. I believe
that this case is harder to hit (and did not hit in my testing),
in that over the tcp 'soft' memory limits, we continue to guarantee a
minimum write buffer size. Perhaps, we could return -ENOSPC in this
case, or maybe we simply issue a wakeup in this case, such that we
keep retrying the write. Note that this case is not specific to
epoll() ET, but rather would affect blocking sockets as well. So I
view this patch as bringing epoll() edge-trigger into sync with the
current poll()/select()/epoll() level trigger and blocking sockets
behavior.

Signed-off-by: Jason Baron 
Acked-by: Eric Dumazet 
Signed-off-by: David S. Miller

net: replace macros net_random and net_srandom with direct calls to prandom

2014-01-14T23:15:25+00:00

This patch removes the net_random and net_srandom macros and replaces
them with direct calls to the prandom ones. As new commits only seem to
use prandom_u32 there is no use to keep them around.
This change makes it easier to grep for users of prandom_u32.

Signed-off-by: Aruna-Hewapathirane 
Suggested-by: Hannes Frederic Sowa 
Acked-by: Hannes Frederic Sowa 
Signed-off-by: David S. Miller

net: add sk_stream_is_writeable() helper

2013-07-25T00:54:48+00:00

Several call sites use the hardcoded following condition :

sk_stream_wspace(sk) >= sk_stream_min_wspace(sk)

Lets use a helper because TCP_NOTSENT_LOWAT support will change this
condition for TCP sockets.

Signed-off-by: Eric Dumazet 
Cc: Neal Cardwell 
Cc: Yuchung Cheng 
Acked-by: Neal Cardwell 
Signed-off-by: David S. Miller

net: Fix the condition passed to sk_wait_event()

2010-10-04T03:41:32+00:00

This patch fixes the condition (3rd arg) passed to sk_wait_event() in
sk_stream_wait_memory(). The incorrect check in sk_stream_wait_memory()
causes the following soft lockup in tcp_sendmsg() when the global tcp
memory pool has exhausted.

>>> snip <<<

localhost kernel: BUG: soft lockup - CPU#3 stuck for 11s! [sshd:6429]
localhost kernel: CPU 3:
localhost kernel: RIP: 0010:[sk_stream_wait_memory+0xcd/0x200]  [sk_stream_wait_memory+0xcd/0x200] sk_stream_wait_memory+0xcd/0x200
localhost kernel:
localhost kernel: Call Trace:
localhost kernel:  [sk_stream_wait_memory+0x1b1/0x200] sk_stream_wait_memory+0x1b1/0x200
localhost kernel:  [] autoremove_wake_function+0x0/0x40
localhost kernel:  [ipv6:tcp_sendmsg+0x6e6/0xe90] tcp_sendmsg+0x6e6/0xce0
localhost kernel:  [sock_aio_write+0x126/0x140] sock_aio_write+0x126/0x140
localhost kernel:  [xfs:do_sync_write+0xf1/0x130] do_sync_write+0xf1/0x130
localhost kernel:  [] autoremove_wake_function+0x0/0x40
localhost kernel:  [hrtimer_start+0xe3/0x170] hrtimer_start+0xe3/0x170
localhost kernel:  [vfs_write+0x185/0x190] vfs_write+0x185/0x190
localhost kernel:  [sys_write+0x50/0x90] sys_write+0x50/0x90
localhost kernel:  [system_call+0x7e/0x83] system_call+0x7e/0x83

>>> snip <<<

What is happening is, that the sk_wait_event() condition passed from
sk_stream_wait_memory() evaluates to true for the case of tcp global memory
exhaustion. This is because both sk_stream_memory_free() and vm_wait are true
which causes sk_wait_event() to *not* call schedule_timeout().
Hence sk_stream_wait_memory() returns immediately to the caller w/o sleeping.
This causes the caller to again try allocation, which again fails and again
calls sk_stream_wait_memory(), and so on.

[ Bug introduced by commit c1cbe4b7ad0bc4b1d98ea708a3fecb7362aa4088
  ("[NET]: Avoid atomic xchg() for non-error case") -DaveM ]

Signed-off-by: Nagendra Singh Tomar 
Signed-off-by: David S. Miller

net/core: EXPORT_SYMBOL cleanups

2010-07-12T19:57:55+00:00

CodingStyle cleanups

EXPORT_SYMBOL should immediately follow the symbol declaration.

Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

net: sock_def_readable() and friends RCU conversion

2010-05-01T22:00:15+00:00

sk_callback_lock rwlock actually protects sk->sk_sleep pointer, so we
need two atomic operations (and associated dirtying) per incoming
packet.

RCU conversion is pretty much needed :

1) Add a new structure, called "struct socket_wq" to hold all fields
that will need rcu_read_lock() protection (currently: a
wait_queue_head_t and a struct fasync_struct pointer).

[Future patch will add a list anchor for wakeup coalescing]

2) Attach one of such structure to each "struct socket" created in
sock_alloc_inode().

3) Respect RCU grace period when freeing a "struct socket_wq"

4) Change sk_sleep pointer in "struct sock" by sk_wq, pointer to "struct
socket_wq"

5) Change sk_sleep() function to use new sk->sk_wq instead of
sk->sk_sleep

6) Change sk_has_sleeper() to wq_has_sleeper() that must be used inside
a rcu_read_lock() section.

7) Change all sk_has_sleeper() callers to :
  - Use rcu_read_lock() instead of read_lock(&sk->sk_callback_lock)
  - Use wq_has_sleeper() to eventually wakeup tasks.
  - Use rcu_read_unlock() instead of read_unlock(&sk->sk_callback_lock)

8) sock_wake_async() is modified to use rcu protection as well.

9) Exceptions :
  macvtap, drivers/net/tun.c, af_unix use integrated "struct socket_wq"
instead of dynamically allocated ones. They dont need rcu freeing.

Some cleanups or followups are probably needed, (possible
sk_callback_lock conversion to a spinlock for example...).

Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

net: sk_sleep() helper

2010-04-20T23:37:13+00:00

Define a new function to return the waitqueue of a "struct sock".

static inline wait_queue_head_t *sk_sleep(struct sock *sk)
{
	return sk->sk_sleep;
}

Change all read occurrences of sk_sleep by a call to this function.

Needed for a future RCU conversion. sk_sleep wont be a field directly
available.

Signed-off-by: Eric Dumazet 
Signed-off-by: David S. Miller

tcp: tcp_prequeue() can use keyed wakeups

2009-05-18T03:44:43+00:00

When TCP frees up write buffer space, avoid waking up tasks that have
done a poll() or select() on the same socket specifying read-side
events.

This is an extension of a read-side patch by Eric Dumazet.

Signed-off-by: John Dykstra 
Acked-by: Eric Dumazet 
Signed-off-by: David S. Miller

net: Rationalise email address: Network Specific Parts

2008-10-14T02:01:08+00:00

Clean up the various different email addresses of mine listed in the code
to a single current and valid address. As Dave says his network merges
for 2.6.28 are now done this seems a good point to send them in where
they won't risk disrupting real changes.

Signed-off-by: Alan Cox 
Signed-off-by: David S. Miller

net: convert BUG_TRAP to generic WARN_ON

2008-07-26T04:43:18+00:00

Removes legacy reinvent-the-wheel type thing. The generic
machinery integrates much better to automated debugging aids
such as kerneloops.org (and others), and is unambiguous due to
better naming. Non-intuively BUG_TRAP() is actually equal to
WARN_ON() rather than BUG_ON() though some might actually be
promoted to BUG_ON() but I left that to future.

I could make at least one BUILD_BUG_ON conversion.

Signed-off-by: Ilpo Järvinen 
Signed-off-by: David S. Miller