[LU-20291] Direct I/O broken on Lustre client with Linux 6.18+

• Type: Bug
• Resolution: Duplicate
• Priority: Major
• Severity: 3
• Assignee: WC Triage
• Reporter: Sohei Koyama

Description

On Linux 7.0 6.18 and later kernels, Lustre client Direct I/O is broken.
All O_DIRECT writes and reads on a Lustre mount return -EINVAL even when
the user buffer and file offset are properly page-aligned.

 

Steps to reproduce:

1. Mount a Lustre filesystem on a client running Linux 7.0+ 6.18+ (e.g. Ubuntu 26.04)
2. Disable unaligned_dio:

   lctl set_param llite.*.unaligned_dio=0 

1. Perform an O_DIRECT write with a page-aligned buffer:

   fd = open("testfile", O_WRONLY|O_CREAT|O_DIRECT, 0644);
   posix_memalign(&buf, 4096, 4096);
   n = write(fd, buf, 4096);
   // Returns -1, errno=EINVAL
   

Root cause

The compat shim for iov_iter_is_aligned() in include/lustre_compat/linux/uio.h incorrectly checks the kernel stack address instead of the user buffer address for ITER_UBUF iterators,
causing all aligned buffers to be misidentified as unaligned. The compat shim is used on Linux 7.0+ 6.18+ where iov_iter_is_aligned() is no longer available.

 

Issue Links

• is related to: LU-19526 iov_iter_is_aligned() should be checking actual buffer address