Re: panic: bremfree: removing a buffer not on a queue (again)

> I'm getting fully repeatable crashes on an nfs server running -current,
> with a 4.6-release nfs client.  This has been happening for some while,
> and the last crash was with kernel/world built from sources cvsupped
> yesterday.  The client was running a buildworld with both obj and src
> mounted over nfs.  The server was otherwise quiet, and had recently
> undergone a full, clean fsck.  The server runs an smp kernel with 2
> cpu's.


I've attached a tcpdump of the NFS activity leading up to a crash of 
this type which occurred some time between 22:25:47 and 22:25:54 in the 
time-line below.  The buildworld had got as far as building 
contrib/groff/src/roff/troff/input.cc

192.168.100.1 is the 4.6-release client, and .44 is the 5.1-beta server.

Nick

22:25:47.890909 192.168.100.1.1128420554 > 192.168.100.44.2049: 136 lookup [|nfs]
                         4500 00a4 16d8 0000 4011 0000 c0a8 6401
                         c0a8 642c 03ea 0801 0090 d8cc 4342 54ca
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0003 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:47.891179 192.168.100.44.2049 > 192.168.100.1.1128420554: reply ok 116 lookup ERROR: No such file or directo
ry
                         4500 0090 9b2b 0000 4011 95b3 c0a8 642c
                         c0a8 6401 0801 03ea 007c 8f1b 4342 54ca
                         0000 0001 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0002 0000 0001 0000 0002
                         0000 01ed 0000 0002 0000 00cc 0000 0000
                         0000
22:25:47.891542 192.168.100.1.1128420555 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 16d9 0000 4011 0000 c0a8 6401
                         c0a8 642c 03ea 0801 0084 998f 4342 54cb
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:47.891806 192.168.100.44.2049 > 192.168.100.1.1128420555: reply ok 120 access c 4342536b
                         4500 0094 9b2c 0000 4011 95ae c0a8 642c
                         c0a8 6401 0801 03ea 0080 6759 4342 54cb
                         0000 0001 0000 0000 0000 0000 0000 0000
                         0000 0000 0000 0000 0000 0001 0000 0001
                         0000 01a4 0000 0001 0000 00cc 0000 0000
                         0000
22:25:54.212203 192.168.100.1.1128420556 > 192.168.100.44.2049: 132 commit [|nfs]
                         4500 00a0 1772 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 008c 755f 4342 54cc
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0015 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:54.625787 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 1777 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:54.671795 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 1778 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:54.761721 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 1779 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:54.931739 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 177e 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:55.261827 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 1783 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000
22:25:55.911853 192.168.100.1.1128420557 > 192.168.100.44.2049: 124 access [|nfs]
                         4500 0098 17b9 0000 4011 0000 c0a8 6401
                         c0a8 642c 03e5 0801 0084 5704 4342 54cd
                         0000 0000 0000 0002 0001 86a3 0000 0003
                         0000 0004 0000 0001 0000 0030 0000 0000
                         0000 0000 0000 0000 0000 0000 0000 0007
                         0000