mm/slab: pass alloc_flags through slab_post_alloc_hook() chain

mm/slab: pass alloc_flags through slab_post_alloc_hook() chain

Convert the whole following call stack to pass either slab_alloc_context
(thus including alloc_flags) or just alloc_flags as necessary:

slab_post_alloc_hook()
  alloc_tagging_slab_alloc_hook()
    __alloc_tagging_slab_alloc_hook()
      prepare_slab_obj_exts_hook()
        alloc_slab_obj_exts()
  memcg_slab_post_alloc_hook()
    __memcg_slab_post_alloc_hook()
      alloc_slab_obj_exts()

Converting all these at once avoids unnecessary churn and is mostly
mechanical.

This ultimately allows to decide if spinning is allowed using
alloc_flags in alloc_slab_obj_exts(), as well as slab_post_alloc_hook().
Aside from alloc_from_pcs_bulk() (to be handled next) there is nothing
else in slab itself relying on gfpflags_allow_spinning() which can
be false even if not called from kmalloc_nolock().

A followup change will also use the alloc_flags availability in the call
stack above to remove the __GFP_NO_OBJ_EXT flag.

For alloc_slab_obj_exts(), also replace the suboptimal "bool new_slab"
parameter with a SLAB_ALLOC_NEW_SLAB flag with identical functionality.

To further reduce the number of parameters of slab_post_alloc_hook(),
also make 'struct list_lru *lru' (which is NULL for most callers) a new
field of slab_alloc_context.

Link: https://patch.msgid.link/20260610-slab_alloc_flags-v2-9-7190909db118@kernel.org
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Hao Li <hao.li@linux.dev>
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>