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[ Upstream commit 49beadbd ]

While the concept of checking for dangling pointers to local variables
at function exit is really interesting, the gcc-12 implementation is not
compatible with reality, and results in false positives.

For example, gcc sees us putting things on a local list head allocated
on the stack, which involves exactly those kinds of pointers to the
local stack entry:

  In function ‘__list_add’,
      inlined from ‘list_add_tail’ at include/linux/list.h:102:2,
      inlined from ‘rebuild_snap_realms’ at fs/ceph/snap.c:434:2:
  include/linux/list.h:74:19: warning: storing the address of local variable ‘realm_queue’ in ‘*&realm_27(D)->rebuild_item.prev’ [-Wdangling-pointer=]
     74 |         new->prev = prev;
        |         ~~~~~~~~~~^~~~~~

But then gcc - understandably - doesn't really understand the big
picture how the doubly linked list works, so doesn't see how we then end
up...