Date:	Wed, 26 Feb 2014 13:05:59 -0800
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	netdev@...r.kernel.org
Cc:	karl@....com
Subject: Bug 70021 - Call to munmap() causes system to partially hang; power
 cycle needed to recover.

This bug appears to have been stuck in MM bugzilla and never
addressed...

https://bugzilla.kernel.org/show_bug.cgi?id=70021


[reply] [−]  Private Description Karl Auerbach 2014-02-05 00:51:02 UTC
Created attachment 124531 [details]
This is a small program that triggers the fault.  It requires root privilege to run.

Before kernel 3.12.1 one could mmap() the RX and TX ring buffers for a network socket and reliably release them with munmap().

Starting with kernel 3.12.1 and running through the latest kernel I tested (3.1.14) this no longer works.  The call to munmap() never returns.

Parts of the system may continue to operate, but the system can not be shut down by normal means.  It takes a hardware reset or power cycle to recover.

I've got a short program, extracted from something we've been running for several years, that triggers the problem.

I believe that every kernel from 3.12.1 and forward faults when this is run.

This has been reported to the Fedora crew, and it was suggested that I kick this upstream.  So here I am.

---
#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <unistd.h>

#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/user.h>

#include <features.h>    /* for the glibc version number */
#include <net/ethernet.h>
#include <linux/if_packet.h>
#include <linux/if_ether.h>

#include <net/if.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <linux/if_tun.h>

#define NIL   0

typedef int SOCKET;

int main(int argc, char *argv)
{
size_t              RxMmap_Size;
size_t              TxMmap_Size;
unsigned int        Ether_Sz;
unsigned int        Block_Sz_Order;
unsigned int        Block_Sz;
unsigned int        Block_Cnt;
unsigned int        Frame_Sz;
unsigned int        Frame_Cnt;
unsigned int        Frames_Per_Block;
int                 rcode;

void *              Mmap_Addr;
size_t              Mmap_Size;
size_t		        TXDataOffset;

SOCKET              Socket;

struct tpacket_req ring_req;

Ether_Sz = 1518;
Block_Sz = Ether_Sz;
Block_Sz_Order = 2; // 16384 byte blocks 
Block_Cnt = 1000;

Socket = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
if (Socket == -1)
  {
  perror("socket failed");
  return 1;
  }

Frame_Sz = TPACKET_ALIGN(TPACKET_ALIGN(TPACKET2_HDRLEN) + Ether_Sz);
TXDataOffset = TPACKET2_HDRLEN - sizeof(struct sockaddr_ll);

Block_Sz = getpagesize() << Block_Sz_Order;

Frames_Per_Block = Block_Sz / Frame_Sz;
Frame_Cnt = Frames_Per_Block * Block_Cnt;

RxMmap_Size = Block_Sz * Block_Cnt;
TxMmap_Size = RxMmap_Size;

Mmap_Size = RxMmap_Size + TxMmap_Size;

// Establish receive ring
// For convenience we will let it be the same size as the TX ring
// The mmap size calculations, far above, assume that the
// rings are the same size.
ring_req.tp_block_nr = Block_Cnt;
ring_req.tp_frame_size = Frame_Sz;
ring_req.tp_block_size = Block_Sz;
ring_req.tp_frame_nr = Frame_Cnt;
if (setsockopt(Socket, SOL_PACKET, PACKET_RX_RING,
               (char *)&ring_req, sizeof(ring_req)) < 0)
  {
  perror("Setsockopt RX_RING failed");
  close(Socket);
  return -1;
  }

// Establish transmit ring
// For convenience we will let it be the same size as the RX ring
// The mmap size calculations, far above, assume that the
// rings are the same size.
ring_req.tp_block_nr = Block_Cnt;
ring_req.tp_frame_size = Frame_Sz;
ring_req.tp_block_size = Block_Sz;
ring_req.tp_frame_nr = Frame_Cnt;
if (setsockopt(Socket, SOL_PACKET, PACKET_TX_RING,
               (char *)&ring_req, sizeof(ring_req)) < 0)
  {
  perror("Setsockopt TX_RING failed");
  close(Socket);
  return -1;
  }

fprintf(stderr, "Calling mmap\n");
Mmap_Addr = mmap(NIL, Mmap_Size, PROT_READ | PROT_WRITE,
                 MAP_SHARED | MAP_LOCKED, Socket, 0);

if (Mmap_Addr == MAP_FAILED)
  {
  perror("mmap failed");
  return 1;
  }

fprintf(stderr, "Calling munmap\n");
if (Mmap_Addr != MAP_FAILED)
  {
  if (munmap(Mmap_Addr, Mmap_Size) != 0)
     {
     perror("munmap failed");
     return 1;
     }
  }

fprintf(stderr, "Closing socket\n");
if (close(Socket) != 0)
  {
  perror("close failed");
  return 1;
  }

fprintf(stderr, "Program returning\n");
return 0;
}
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