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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id t78-20020a25aad4000000b00bcd91bb300esm1448109ybi.54.2023.09.02.08.29.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 02 Sep 2023 08:29:58 -0700 (PDT) Date: Sat, 2 Sep 2023 08:29:30 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@ripple.attlocal.net To: Linus Torvalds cc: Andrew Morton , Mikhail Gavrilov , Dave Hansen , Bagas Sanjaya , linux-kernel@vger.kernel.org, linux-mm@kvack.org, regressions@lists.linux.dev Subject: [PATCH] mm/pagewalk: fix bootstopping regression from extra pte_unmap() Message-ID: <8321a347-4a38-526c-97fb-5999ceaf6dd@google.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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=3Dy. Gaah, that added an "addr >=3D 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 Closes: https://lore.kernel.org/linux-mm/CABXGCsNi8Tiv5zUPNXr6UJw6qV1VdaBEf= GqEAMkkXE3QPvZuAQ@mail.gmail.com/ 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 Tested-by: Mikhail Gavrilov --- mm/pagewalk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/pagewalk.c b/mm/pagewalk.c index 9b2d23fbf4d3..b7d7e4fcfad7 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 =3D pte_offset_map(pmd, addr); if (pte) { err =3D walk_pte_range_inner(pte, addr, end, walk); - if (walk->mm !=3D &init_mm) + if (walk->mm !=3D &init_mm && addr < TASK_SIZE) pte_unmap(pte); } } else { --=20 2.35.3