mbox series

[0/3] fs/9p: fix mmap regression

Message ID 20230716-fixes-overly-restrictive-mmap-v1-0-0683b283b932@kernel.org
Headers
Series fs/9p: fix mmap regression |

Message

Eric Van Hensbergen July 17, 2023, 4:28 p.m. UTC 
  This series attempts to fix a reported exception with mmap
on newer kernels. 

-- original regression report --

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.

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

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.

-- end bug report --

Reported-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Eric Van Hensbergen <ericvh@kernel.org>
---
Eric Van Hensbergen (3):
      fs/9p: remove unecessary and overrestrictive check
      fs/9p: fix typo in comparison logic for cache mode
      fs/9p: fix type mismatch in file cache mode helper

 fs/9p/fid.h      | 6 +++---
 fs/9p/vfs_file.c | 2 --
 2 files changed, 3 insertions(+), 5 deletions(-)
---
base-commit: 95f41d87810083d8b3dedcce46a4e356cf4a9673
change-id: 20230716-fixes-overly-restrictive-mmap-30a23501e787

Best regards,

Comments

Linux regression tracking (Thorsten Leemhuis) July 19, 2023, 2:17 p.m. UTC | #1 
On 17.07.23 18:28, Eric Van Hensbergen wrote:
> This series attempts to fix a reported exception with mmap
> on newer kernels. 
> 
> -- original regression report --
> 
> 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.
>
> [...]
> 
> I could track down the breakage to
> 
>   1543b4c5071c54d76aad7a7a26a6e43082269b0c
> 
> 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.
> 
> -- end bug report --
> 
> Reported-by: Robert Schwebel <r.schwebel@pengutronix.de>

This tag afaics should be in some or all of the commits -- together with
a Link: or Closes: tag to the report
(https://lore.kernel.org/v9fs/ZK25XZ%2BGpR3KHIB%2F@pengutronix.de/ ).

'Fixes:' tags would seem appropriate here as well. And to get this fixed
in Linux 6.4.y. a "Cc: <stable..." would be great as well.

See Documentation/handling-regressions.rst (
https://docs.kernel.org/process/handling-regressions.html ) and the
links to Documentation/process/submitting-patches.rst or
Documentation/process/5.Posting.rst for details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
If I did something stupid, please tell me, as explained on that page.

#regzbot ^backmonitor:
https://lore.kernel.org/v9fs/ZK25XZ%2BGpR3KHIB%2F@pengutronix.de/