powerpc/radix: acquire the pmap lock in mmu_radix_extract()HEADmain

mmu_radix_extract() walks the page tables without holding the pmap lock,
unlike its hash MMU counterpart moea64_extract(). A concurrent unmap can
free and recycle the page table page being walked, so the read returns
whatever now occupies that memory and the caller gets a physical address
that never existed.

That is how mmu_radix_sync_icache() came to hand a bogus address to
__syncicache() and panic the machine. Commit 1574ca1955f5 worked around
it by taking the pmap lock in mmu_radix_sync_icache(), but the machine
independent callers of pmap_extract() - vm_sync_icache(), proc_rwmem()
and the vslock() paths - remain exposed to the same failure.

Rename the existing body to mmu_radix_extract_locked(), which asserts the
lock, and make mmu_radix_extract() a thin wrapper that acquires it.
mmu_radix_sync_icache() already holds the pmap lock, so it calls the
locked variant directly and neither recurses nor reacquires the lock once
per page.

Suggested by:	alc
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D59320
Reviewed by:	markj, jhibbits

0 files changed, 0 insertions, 0 deletions