Is this a problem in GenericXLogFinish()?

src/backend/transam/README says:

...
4. Mark the shared buffer(s) as dirty with MarkBufferDirty(). (This 
must happen before the WAL record is inserted; see notes in 
SyncOneBuffer().)
...

But GenericXLogFinish() does this:

...
/* Insert xlog record */
lsn = XLogInsert(RM_GENERIC_ID, 0);

/* Set LSN and mark buffers dirty */
for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
{
PageData *pageData = &state->pages[i];

if (BufferIsInvalid(pageData->buffer))
continue;
PageSetLSN(BufferGetPage(pageData->buffer), lsn);
MarkBufferDirty(pageData->buffer);
}
END_CRIT_SECTION();

Am I missing something or is that a problem?

Regards,
Jeff Davis