Commits on Oct 2, 2024

1. Always validate checksums for Direct I/O reads …

   This fixes an oversight in the Direct I/O PR. There is nothing stops a
   process from manipulating the contents of a buffer for a Direct I/O read
   while the I/O is in flight. This can lead checksum verify failures.
   However, the disk contents are stil correct, but this would lead false
   reporting of checksum validations.
   
   To remedy this, all Direct I/O reads that have a checksum verification
   failure are treated as suspicious. In the event a checksum validation
   failure occurs for a Direct I/O read, then the I/O request will be
   reissued though the ARC. This allows for actual validation to happen and
   removes any possibility of the buffer being manipulated after the I/O
   has been issued.
   
   Just as with Direct I/O write checksum validation failures, Direct I/O
   read checksum validation failures are reported though zpool status -d in
   the DIO columnm. Also the zevent has been updated to have both:
   1. dio_verify_wr -> Checksum verification failure for writes
   2. dio_verify_rd -> Checksum verification failure for reads.
   This allows for determining what I/O operation was the culprit for the
   checksum verification failure. All DIO errors are reported only on the
   top-level VDEV.
   
   Even though FreeBSD can write protect pages (stable pages) it still has
   the same issue as Linux in department.
   
   This commit updates the following:
   1. Propogates checksum failures for reads all the way up to the
      top-level VDEV.
   2. Reports errors through zpool status -d as DIO.
   3. Has two zevents for checksum verify errors with Direct I/O. One for
      read and one for write.
   4. Updates FreeBSD ABD code to also check for ABD_FLAG_FROM_PAGES and
      handle ABD buffer contents validation the same as Linux.
   5. Moves the declartion of nbytes in zfs_read() to the top of the
      function and outside of the while loop. This was needed due to a
      compliation failure in FreeBSD.
   6. Updated manipulate_user_buffer.c to also manipulate a buffer while a
      Direct I/O read is taking place.
   7. Adds a new test case dio_read_verify that stress tests the new code.
   
   This issue was first observed when installing a Windows 11 VM on a ZFS
   dataset with the dataset property direct set to always. The zpool
   devices would report checksum failures, but running a subsequent zpool
   scrub would not repair any data and report no errors.
   
   Signed-off-by: Brian Atkinson <[email protected]>

   

   bwatkinson committed Oct 2, 2024
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