+22
−21
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connector: fix out-of-order cn_proc netlink message delivery
The proc connector messages include a sequence number, allowing userspace
programs to detect lost messages. However, performing this detection is
currently more difficult than necessary, since netlink messages can be
delivered to the application out-of-order. To fix this, leave pre-emption
disabled during cn_netlink_send(), and use GFP_NOWAIT.
The following was written as a test case. Building the kernel w/ make -j32
proved a reliable way to generate out-of-order cn_proc messages.
int
main(int argc, char *argv[])
{
static uint32_t last_seq[CPU_SETSIZE], seq;
int cpu, fd;
struct sockaddr_nl sa;
struct __attribute__((aligned(NLMSG_ALIGNTO))) {
struct nlmsghdr nl_hdr;
struct __attribute__((__packed__)) {
struct cn_msg cn_msg;
struct proc_event cn_proc;
};
} rmsg;
struct __attribute__((aligned(NLMSG_ALIGNTO))) {
struct nlmsghdr nl_hdr;
struct __attribute__((__packed__)) {
struct cn_msg cn_msg;
enum proc_cn_mcast_op cn_mcast;
};
} smsg;
fd = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
if (fd < 0) {
perror("socket");
}
sa.nl_family = AF_NETLINK;
sa.nl_groups = CN_IDX_PROC;
sa.nl_pid = getpid();
if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
perror("bind");
}
memset(&smsg, 0, sizeof(smsg));
smsg.nl_hdr.nlmsg_len = sizeof(smsg);
smsg.nl_hdr.nlmsg_pid = getpid();
smsg.nl_hdr.nlmsg_type = NLMSG_DONE;
smsg.cn_msg.id.idx = CN_IDX_PROC;
smsg.cn_msg.id.val = CN_VAL_PROC;
smsg.cn_msg.len = sizeof(enum proc_cn_mcast_op);
smsg.cn_mcast = PROC_CN_MCAST_LISTEN;
if (send(fd, &smsg, sizeof(smsg), 0) != sizeof(smsg)) {
perror("send");
}
while (recv(fd, &rmsg, sizeof(rmsg), 0) == sizeof(rmsg)) {
cpu = rmsg.cn_proc.cpu;
if (cpu < 0) {
continue;
}
seq = rmsg.cn_msg.seq;
if ((last_seq[cpu] != 0) && (seq != last_seq[cpu] + 1)) {
printf("out-of-order seq=%d on cpu=%d\n", seq, cpu);
}
last_seq[cpu] = seq;
}
/* NOTREACHED */
perror("recv");
return -1;
}
Signed-off-by: 
Aaron Campbell <aaron@monkey.org>
Signed-off-by: David S. Miller <davem@davemloft.net>