From: Oscar Salvador <osalvador@suse.de>
To: Jane Chu <jane.chu@oracle.com>
Cc: david@redhat.com, harry.yoo@oracle.com, liushixin2@huawei.com,
muchun.song@linux.dev, akpm@linux-foundation.org,
jannh@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 RESEND] mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count
Date: Wed, 17 Sep 2025 10:18:47 +0200 [thread overview]
Message-ID: <aMpu58yNnLWszoqX@localhost.localdomain> (raw)
In-Reply-To: <20250916191252.1653993-1-jane.chu@oracle.com>
On Tue, Sep 16, 2025 at 01:12:52PM -0600, Jane Chu wrote:
> commit 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count")
> introduced ->pt_share_count dedicated to hugetlb PMD share count tracking,
> but omitted fixing copy_hugetlb_page_range(), leaving the function relying on
> page_count() for tracking that no longer works.
>
> When lazy page table copy for hugetlb is disabled, that is, revert
> commit bcd51a3c679d ("hugetlb: lazy page table copies in fork()")
> fork()'ing with hugetlb PMD sharing quickly lockup -
>
> [ 239.446559] watchdog: BUG: soft lockup - CPU#75 stuck for 27s!
> [ 239.446611] RIP: 0010:native_queued_spin_lock_slowpath+0x7e/0x2e0
> [ 239.446631] Call Trace:
> [ 239.446633] <TASK>
> [ 239.446636] _raw_spin_lock+0x3f/0x60
> [ 239.446639] copy_hugetlb_page_range+0x258/0xb50
> [ 239.446645] copy_page_range+0x22b/0x2c0
> [ 239.446651] dup_mmap+0x3e2/0x770
> [ 239.446654] dup_mm.constprop.0+0x5e/0x230
> [ 239.446657] copy_process+0xd17/0x1760
> [ 239.446660] kernel_clone+0xc0/0x3e0
> [ 239.446661] __do_sys_clone+0x65/0xa0
> [ 239.446664] do_syscall_64+0x82/0x930
> [ 239.446668] ? count_memcg_events+0xd2/0x190
> [ 239.446671] ? syscall_trace_enter+0x14e/0x1f0
> [ 239.446676] ? syscall_exit_work+0x118/0x150
> [ 239.446677] ? arch_exit_to_user_mode_prepare.constprop.0+0x9/0xb0
> [ 239.446681] ? clear_bhb_loop+0x30/0x80
> [ 239.446684] ? clear_bhb_loop+0x30/0x80
> [ 239.446686] entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> There are two options to resolve the potential latent issue:
> 1. warn against PMD sharing in copy_hugetlb_page_range(),
> 2. fix it.
> This patch opts for the second option.
> While at it, simplify the comment, the details are not actually relevant
> anymore.
>
> Fixes: 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count")
> Signed-off-by: Jane Chu <jane.chu@oracle.com>
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Thanks
--
Oscar Salvador
SUSE Labs
prev parent reply other threads:[~2025-09-17 8:18 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-16 19:12 Jane Chu
2025-09-17 8:18 ` Oscar Salvador [this message]
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