• Nagendra Tomar's avatar
    net: Fix the condition passed to sk_wait_event() · 482964e5
    Nagendra Tomar authored
    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:  [<ffffffff802557c0>] 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:  [<ffffffff802557c0>] 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 c1cbe4b7
    
    
      ("[NET]: Avoid atomic xchg() for non-error case") -DaveM ]
    Signed-off-by: default avatarNagendra Singh Tomar <tomer_iisc@yahoo.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    482964e5