[Deepin-Kernel-SIG] [linux 6.6-y] [FROMLIST] mm/mempolicy: fix unbalanced unlock in backported VMA check

[opsiff]

No upstream commit exists for this commit.

The issue was introduced with backporting upstream commit 091c1dd ("mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM").

The backport incorrectly added unlock logic to a path where mmap_read_lock() wasn't acquired, creating lock imbalance when no VMAs are found.

This fixes the report:

WARNING: bad unlock balance detected!
6.6.79 #1 Not tainted

repro/9655 is trying to release lock (&mm->mmap_lock) at: [] mmap_read_unlock include/linux/mmap_lock.h:173 [inline] [] do_migrate_pages+0x59f/0x700 mm/mempolicy.c:1196 but there are no more locks to release!

other info that might help us debug this:
no locks held by repro/9655.

stack backtrace:
CPU: 1 PID: 9655 Comm: a Not tainted 6.6.79 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Call Trace:

__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd5/0x1b0 lib/dump_stack.c:106
__lock_release kernel/locking/lockdep.c:5431 [inline]
lock_release+0x4b1/0x680 kernel/locking/lockdep.c:5774
up_read+0x12/0x20 kernel/locking/rwsem.c:1615
mmap_read_unlock include/linux/mmap_lock.h:173 [inline]
do_migrate_pages+0x59f/0x700 mm/mempolicy.c:1196
kernel_migrate_pages+0x59b/0x780 mm/mempolicy.c:1665
__do_sys_migrate_pages mm/mempolicy.c:1684 [inline]
__se_sys_migrate_pages mm/mempolicy.c:1680 [inline]
__x64_sys_migrate_pages+0x92/0xf0 mm/mempolicy.c:1680
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x34/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: a13b2b9 ("mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM")

Summary by Sourcery

Bug Fixes:

• Fixes a lock imbalance in the memory management code that occurs when no VMAs are found.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request fixes a lock imbalance issue introduced by a backport of a memory management patch. The original backport incorrectly added unlock logic to a code path where the corresponding lock was not acquired, leading to a 'bad unlock balance' warning. This PR removes the extraneous unlock to resolve the imbalance.

No diagrams generated as the changes look simple and do not need a visual representation.

File-Level Changes

Change	Details	Files
Remove an unnecessary mmap_read_unlock call to fix a lock imbalance.	Removed the call to mmap_read_unlock(mm) within the if (unlikely(!vma)) block in migrate_to_node.	mm/mempolicy.c

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在migrate_to_node函数中，移除了mmap_read_unlock(mm);的调用，但未提供替代逻辑或说明原因。

是否建议立即修改:

• 是，需要确认移除mmap_read_unlock(mm);的原因，并确保不会影响其他部分的并发访问控制。如果移除是有意为之，应该添加相应的注释说明原因。如果移除是无意的，应该立即恢复该调用。

[sourcery-ai]

Hey @opsiff - I've reviewed your changes - here's some feedback:

Overall Comments:

• Good catch on identifying and fixing the lock imbalance issue introduced by the backport!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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