nix-collect-garbage Bus error

[aragnon]

Assumptions:
-/nix is on the same file system as /
-the file system holding / has no space available

In this state, run nix-collect-garbage.

The result is:

Core was generated by `/usr/bin/nix-store --gc'.
Program terminated with signal 7, Bus error.
#0 0x00007fd87a46c939 in ?? ()

(gdb) bt
#0 0x00007fd87a46c939 in ?? ()
#1 0x0000000000d6b1f8 in ?? ()
#2 0x0000000000000000 in ?? ()

[edolstra]

Can you run "nix-store --gc -vvvv"?

[edolstra]

Also, what platform is this?

[aragnon]

Do the following to reproduce this:

dd if=/dev/urandom of=/x

(this will exit when your file system is full)

Now do: $ nix-store --gc -vvvv

On my machine this gives no output other than the Bus error mentioned in my first message.

Platform: Ubuntu Precise, x86-64

[edolstra]

What Nix version is this? I've seen SQLite segfault if the disk is full, but Nix reserves some disk space (in /nix/var/nix/db/reserved) that it can delete prior to opening the SQLite DB for this reason.

[aragnon]

(Nix) 1.1

Have you actually followed my instructions?

[viric]

SIGBUS should come mainly from misaligned memory accesses. In x86-64, I think that can happen only using SIMD instructions that require aligned memory pointers with unaligned memory pointers. I don't think there is any SIMD in all what nix runs, apart from glibc's memset or memcpy, that should be properly protected about alignments.

Aragnon, can you disassemble in gdb at the sigbus location, and print 'info registers' to see what happened?

[edolstra]

Closing because I can't reproduce. If the reserved file doesn't exist and the disk is full, I get error: setting synchronous mode: disk I/O error from SQLite.