6.6-stable review patch. If anyone has any objections, please let me know.
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From: Yang Shi yang@os.amperecomputing.com
commit f52ce0ea90c83a28904c7cc203a70e6434adfecb upstream.
When calling mprotect() to a large hugetlb memory area in our customer's workload (~300GB hugetlb memory), soft lockup was observed:
watchdog: BUG: soft lockup - CPU#98 stuck for 23s! [t2_new_sysv:126916]
CPU: 98 PID: 126916 Comm: t2_new_sysv Kdump: loaded Not tainted 6.17-rc7 Hardware name: GIGACOMPUTING R2A3-T40-AAV1/Jefferson CIO, BIOS 5.4.4.1 07/15/2025 pstate: 20400009 (nzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) pc : mte_clear_page_tags+0x14/0x24 lr : mte_sync_tags+0x1c0/0x240 sp : ffff80003150bb80 x29: ffff80003150bb80 x28: ffff00739e9705a8 x27: 0000ffd2d6a00000 x26: 0000ff8e4bc00000 x25: 00e80046cde00f45 x24: 0000000000022458 x23: 0000000000000000 x22: 0000000000000004 x21: 000000011b380000 x20: ffff000000000000 x19: 000000011b379f40 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : ffffc875e0aa5e2c x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 x5 : fffffc01ce7a5c00 x4 : 00000000046cde00 x3 : fffffc0000000000 x2 : 0000000000000004 x1 : 0000000000000040 x0 : ffff0046cde7c000
Call trace: mte_clear_page_tags+0x14/0x24 set_huge_pte_at+0x25c/0x280 hugetlb_change_protection+0x220/0x430 change_protection+0x5c/0x8c mprotect_fixup+0x10c/0x294 do_mprotect_pkey.constprop.0+0x2e0/0x3d4 __arm64_sys_mprotect+0x24/0x44 invoke_syscall+0x50/0x160 el0_svc_common+0x48/0x144 do_el0_svc+0x30/0xe0 el0_svc+0x30/0xf0 el0t_64_sync_handler+0xc4/0x148 el0t_64_sync+0x1a4/0x1a8
Soft lockup is not triggered with THP or base page because there is cond_resched() called for each PMD size.
Although the soft lockup was triggered by MTE, it should be not MTE specific. The other processing which takes long time in the loop may trigger soft lockup too.
So add cond_resched() for hugetlb to avoid soft lockup.
Link: https://lkml.kernel.org/r/20250929202402.1663290-1-yang@os.amperecomputing.c... Fixes: 8f860591ffb2 ("[PATCH] Enable mprotect on huge pages") Signed-off-by: Yang Shi yang@os.amperecomputing.com Tested-by: Carl Worth carl@os.amperecomputing.com Reviewed-by: Christoph Lameter (Ampere) cl@gentwo.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com Acked-by: David Hildenbrand david@redhat.com Acked-by: Oscar Salvador osalvador@suse.de Reviewed-by: Anshuman Khandual anshuman.khandual@arm.com Reviewed-by: Dev Jain dev.jain@arm.com Cc: Muchun Song muchun.song@linux.dev Cc: Will Deacon will@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/hugetlb.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -6693,6 +6693,8 @@ long hugetlb_change_protection(struct vm psize); } spin_unlock(ptl); + + cond_resched(); } /* * Must flush TLB before releasing i_mmap_rwsem: x86's huge_pmd_unshare