Fails xfstests generic/257, panic: underflow: handle 170, count 6, object -1

[hanwen]

Fails xfstests generic/257, panic: underflow: handle 170, count 6, object -1

[hanwen]

whoops, that sounds very serious.

[hanwen]

can you show the entire stack trace? How reproducible is this? What if you compile loopback with the race detector?

[hanwen]

can you see if the problem goes away if you disable readdirplus,

    server.kernelSettings.Flags = input.Flags & (CAP_ASYNC_READ | CAP_BIG_WRITES | CAP_FILE_OPS |
            CAP_AUTO_INVAL_DATA | CAP_READDIRPLUS)

remove CAP_READDIRPLUS from this opcode.go

I suspect the following happens: readdir folds lookup and readdir into one roundtrip. If you mix this with seeking on directories, it's not obvious when to set the lookup count of inodes, because the FUSE process does the entire readdir up front, but the kernel only notices when it consumes the readdir output.

(I wouldn't be surprised if this were in part a kernel bug, btw.)

[rfjakob]

I can trigger this every time I run generic/257. Will check your suggestions tonight and post the full stack trace.

[rfjakob]

Full backtrace: https://gist.github.com/rfjakob/686d05f9fb9681e724c5

Removing CAP_READDIRPLUS fixes the issue, the test passes!