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net: fix multithreaded signal handling in unix recv routines

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The unix_dgram_recvmsg and unix_stream_recvmsg routines in
net/af_unix.c utilize mutex_lock(&u->readlock) calls in order to
serialize read operations of multiple threads on a single socket. This
implies that, if all n threads of a process block in an AF_UNIX recv
call trying to read data from the same socket, one of these threads
will be sleeping in state TASK_INTERRUPTIBLE and all others in state
TASK_UNINTERRUPTIBLE. Provided that a particular signal is supposed to
be handled by a signal handler defined by the process and that none of
this threads is blocking the signal, the complete_signal routine in
kernel/signal.c will select the 'first' such thread it happens to
encounter when deciding which thread to notify that a signal is
supposed to be handled and if this is one of the TASK_UNINTERRUPTIBLE
threads, the signal won't be handled until the one thread not blocking
on the u->readlock mutex is woken up because some data to process has
arrived (if this ever happens). The included patch fixes this by
changing mutex_lock to mutex_lock_interruptible and handling possible
error returns in the same way interruptions are handled by the actual
receive-code.

Signed-off-by: Rainer Weikusat <rweikusat@mobileactivedefense.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Rainer Weikusat 2011-02-28 04:50:55 +00:00 committed by David S. Miller
parent 2ea6d8c446
commit b3ca9b02b0
1 changed files with 13 additions and 4 deletions
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17
net/unix/af_unix.c
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@ -1724,7 +1724,11 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
msg->msg_namelen = 0; msg->msg_namelen = 0;
mutex_lock(&u->readlock); err = mutex_lock_interruptible(&u->readlock);
if (err) {
err = sock_intr_errno(sock_rcvtimeo(sk, noblock));
goto out;
}
skb = skb_recv_datagram(sk, flags, noblock, &err); skb = skb_recv_datagram(sk, flags, noblock, &err);
if (!skb) { if (!skb) {
@ -1864,7 +1868,11 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
memset(&tmp_scm, 0, sizeof(tmp_scm)); memset(&tmp_scm, 0, sizeof(tmp_scm));
} }
mutex_lock(&u->readlock); err = mutex_lock_interruptible(&u->readlock);
if (err) {
err = sock_intr_errno(timeo);
goto out;
}
do { do {
int chunk; int chunk;
@ -1895,11 +1903,12 @@ static int unix_stream_recvmsg(struct kiocb *iocb, struct socket *sock,
timeo = unix_stream_data_wait(sk, timeo); timeo = unix_stream_data_wait(sk, timeo);
if (signal_pending(current)) { if (signal_pending(current)
|| mutex_lock_interruptible(&u->readlock)) {
err = sock_intr_errno(timeo); err = sock_intr_errno(timeo);
goto out; goto out;
} }
mutex_lock(&u->readlock);
continue; continue;
unlock: unlock:
unix_state_unlock(sk); unix_state_unlock(sk);