Re: mmap on 9p broken in 6.4

[Christian Schoenebeck <linux_oss@crudebyte.com>]

On Tuesday, July 11, 2023 10:19:41 PM CEST Robert Schwebel wrote:
> Hi Eric,
> 
> TL;DR: mmap() seems to be broken on 9pfs on Linux 6.4. setting
> "rootflags=ignoreqv" fixes it as well, but it feels like a regression.

What's the precise set of 9p mount options on guest, which 9p server is used
and what are 9p server's options respectively?

> I'm tracking down an issue which recently turned up in DistroKit [1] (an
> embedded Linux distro based on the ptxdist build system). The issue was a bit
> uggly, as my CI didn't find it (systems boot up normally after a while, and I
> only use 9p for virtual qemu machines, while most of the test farm is real
> hardware).
> 
> The qemu machine in question is qemu-system-arm, emulating an ARM v7a machine.
> 
> When starting the systems interactively, I get a lot of error output from
> ldconfig, like this:
> 
> [   17.412964] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libgcc_s.so.1.
> [   17.418851] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libstdc++.so.
> [   17.425009] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libstdc++.so.6.0.30.
> [   17.436671] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libstdc++.so.6.
> [   17.448451] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libatomic.so.
> [   17.456418] systemd-rc-once[127]: ldconfig: Cannot mmap file /lib/libatomic.so.1.2.0.
> ...
> 
> Running ldconfig with strace shows this, for all libraries::
> 
> | statx(AT_FDCWD, "/lib/libnm.so.0", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW|AT_NO_AUTOMOUNT, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFLNK|0777, stx_size=14, ...}) = 0
> | statx(AT_FDCWD, "/lib/libnm.so.0", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|064 4, stx_size=862228, ...}) = 0
> | openat(AT_FDCWD, "/lib/libnm.so.0", O_RDONLY|O_LARGEFILE) = 4
> | statx(4, "", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT|AT_EMPTY_PATH, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_s ize=862228, ...}) = 0
> | mmap2(NULL, 862228, PROT_READ, MAP_SHARED, 4, 0) = -1 ENODEV (No such device)
> | write(2, "ldconfig: ", 10ldconfig: )              = 10
> | write(2, "Cannot mmap file /lib/libnm.so.0"..., 34Cannot mmap file /lib/libnm.so.0.) = 34
> | write(2, "\n", 1)                       = 1
> | close(4)                                = 0
> 
> I could track down the breakage to
> 
>   1543b4c5071c54d76aad7a7a26a6e43082269b0c

This patch is sensitive about 9p server transmitting a meaningful value for
file's QID version field. That's why more info about deployed 9p server would
help.

> My test setup has, in addition to the patch above, the following patches also
> reverted on top of a vanilla 6.4 kernel:
> 
>   4eb3117888a923f6b9b1ad2dd093641c49a63ae5
>   21e26d5e54ab7cfe6b488fd27d4d70956d07e03b
> 
> as 1543b cannot be reverted without those; however, the effect only goes away
> when I also revert 1543b. The kernel has no other patches applied, only these
> three reverts.
> 
> Do you have an idea what happens?
> 
> I have the setup easily available, so I could quickly test patches.
> 
> Thanks,
> 
> rsc
> 
> [1] https://git.pengutronix.de/cgit/DistroKit/
>