mm/pagewalk: fix bootstopping regression from extra pte_unmap()
Mikhail reports early-6.6-based Fedora Rawhide not booting: "rcu_preempt detected expedited stalls", minutes wait, and then hung_task splat while kworker trying to synchronize_rcu_expedited(). Nothing logged to disk. He bisected to my 6.6a349d72fd9
("mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s"): but the one to blame is my 6.5 commit to fix the espfix "bad pmd" warnings when booting x86_64 with CONFIG_EFI_PGT_DUMP=y. Gaah, that added an "addr >= TASK_SIZE" check to avoid pte_offset_map(), but failed to add the equivalent check when choosing to pte_unmap(). It's not a problem on 6.5 (for different reasons, it's harmless on both 64-bit and 32-bit), but becomes a bootstopper on 6.6 with the unbalanced rcu_read_unlock() - RCU has a WARN_ON_ONCE for that, but it would have scrolled off Mikhail's console too quickly. Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> Closes: https://lore.kernel.org/linux-mm/CABXGCsNi8Tiv5zUPNXr6UJw6qV1VdaBEfGqEAMkkXE3QPvZuAQ@mail.gmail.com/ Fixes:8b1cb4a2e8
("mm/pagewalk: fix EFI_PGT_DUMP of espfix area") Fixes:a349d72fd9
("mm/pgtable: add rcu_read_lock() and rcu_read_unlock()s") Signed-off-by: Hugh Dickins <hughd@google.com> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -58,7 +58,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
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pte = pte_offset_map(pmd, addr);
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if (pte) {
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err = walk_pte_range_inner(pte, addr, end, walk);
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if (walk->mm != &init_mm)
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if (walk->mm != &init_mm && addr < TASK_SIZE)
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pte_unmap(pte);
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}
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} else {
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