When running on recent kernel versions, this system call on a cifs-mounted
file sometimes takes an unusually long time:
getxattr("/cifsmount/dir/image.jpg", "user.baloo.rating", NULL, 0)
The call normally returns in under 10 milliseconds, but on kernel 5.14+, it
sometimes takes over 30 seconds with no significant client or server load.
Discovered while using gwenview to browse 100+ 1.5 MiB images on a samba share
mounted via /etc/fstab. While quickly flipping through the images, the problem
often occurs within 20 seconds. Gwenview freezes until the call completes.
Client:
kernel versions 5.14 and later
mount.cifs 6.11
Gwenview 20.12.3
Debian Bullseye
4-core amd64
Server:
Samba 4.13.13-Debian
Debian Bullseye
6-core arm64
A git bisect identified kernel commit 9e992755be8f as the problematic change.
The problem does not occur when any of the following are true:
- Client is running a kernel from before that commit.
- The nouser_xattr mount option is used on the cifs share.
- Gwenview accesses the files via smb:// URL instead of a cifs mount.
I don't know Gwenview's internals, but using its strace output as a guide, I
have written a potential reproducer. It succeeds at triggering slow getxattr()
calls, though not nearly as slow as those triggered by Gwenview. I can post it
if that would be helpful.
