6.5-stable review patch. If anyone has any objections, please let me know.
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From: Hugh Dickins hughd@google.com
[ Upstream commit ee40d543e97d23d3392d8fb1ec9972eb4e9c7611 ]
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 6.6 a349d72fd9ef ("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/CABXGCsNi8Tiv5zUPNXr6UJw6qV1VdaBEfGqEAMkkXE... Fixes: 8b1cb4a2e819 ("mm/pagewalk: fix EFI_PGT_DUMP of espfix area") Fixes: a349d72fd9ef ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- mm/pagewalk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 9b2d23fbf4d35..b7d7e4fcfad7a 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -58,7 +58,7 @@ static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end, pte = pte_offset_map(pmd, addr); if (pte) { err = walk_pte_range_inner(pte, addr, end, walk); - if (walk->mm != &init_mm) + if (walk->mm != &init_mm && addr < TASK_SIZE) pte_unmap(pte); } } else {