CVE-2026-64100 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/msm: Fix shrinker deadlock
With PROVE_LOCKING on an Snapdragon X1 and VM reclaim pressure, we see:
====================================================== WARNING: possible circular locking dependency detected 7.0.0-debug+ #43 Tainted: G W ------------------------------------------------------ kswapd0/82 is trying to acquire lock: ffff800080ec3870 (reservation_ww_class_acquire){+.+.}-{0:0}, at: msm_gem_shrinker_scan+0x17c/0x400 [msm]
but task is already holding lock: ffffc31709b263b8 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x88/0x988
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (fs_reclaim){+.+.}-{0:0}:
__lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 fs_reclaim_acquire+0xd0/0xf0 dma_resv_lockdep+0x224/0x348 do_one_initcall+0x84/0x5d0 do_initcalls+0x194/0x1d8 kernel_init_freeable+0x128/0x180 kernel_init+0x2c/0x160 ret_from_fork+0x10/0x20
-> #1 (reservation_ww_class_mutex){+.+.}-{4:4}:
__lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 dma_resv_lockdep+0x1a8/0x348 do_one_initcall+0x84/0x5d0 do_initcalls+0x194/0x1d8 kernel_init_freeable+0x128/0x180 kernel_init+0x2c/0x160 ret_from_fork+0x10/0x20
-> #0 (reservation_ww_class_acquire){+.+.}-{0:0}:
check_prev_add+0x114/0x790 validate_chain+0x594/0x6f0 __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 drm_gem_lru_scan+0x1ac/0x440 msm_gem_shrinker_scan+0x17c/0x400 [msm]
do_shrink_slab+0x150/0x4a0 shrink_slab+0x144/0x460 shrink_one+0x9c/0x1b0 shrink_many+0x27c/0x5c0 shrink_node+0x344/0x550 balance_pgdat+0x2c0/0x988 kswapd+0x11c/0x318 kthread+0x10c/0x128 ret_from_fork+0x10/0x20
other info that might help us debug this: Chain exists of: reservation_ww_class_acquire --> reservation_ww_class_mutex --> fs_reclaim Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(fs_reclaim); lock(reservation_ww_class_mutex); lock(fs_reclaim); lock(reservation_ww_class_acquire);
*** DEADLOCK *** 1 lock held by kswapd0/82: #0: ffffc31709b263b8 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat+0x88/0x988
stack backtrace: CPU: 4 UID: 0 PID: 82 Comm: kswapd0 Tainted: G W 7.0.0-debug+ #43 PREEMPT(full) Tainted: [W]=WARN
Hardware name: LENOVO 21BX0016US/21BX0016US, BIOS N3HET94W (1.66 ) 09/15/2025 Call trace: show_stack+0x20/0x40 (C) dump_stack_lvl+0x9c/0xd0 dump_stack+0x18/0x30 print_circular_bug+0x114/0x120 check_noncircular+0x178/0x198 check_prev_add+0x114/0x790 validate_chain+0x594/0x6f0 __lock_acquire+0x4d0/0xad0 lock_acquire.part.0+0xc4/0x248 lock_acquire+0x8c/0x248 drm_gem_lru_scan+0x1ac/0x440 msm_gem_shrinker_scan+0x17c/0x400 [msm]
do_shrink_slab+0x150/0x4a0 shrink_slab+0x144/0x460 shrink_one+0x9c/0x1b0 shrink_many+0x27c/0x5c0 shrink_node+0x344/0x550 balance_pgdat+0x2c0/0x988 kswapd+0x11c/0x318 kthread+0x10c/0x128 ret_from_fork+0x10/0x20
kswapd0 holding fs_reclaim calls the MSM shrinker, which calls dma_resv_lock. This in turn acquires fs_reclaim.
Fix this deadlock by using dma_resv_trylock() instead, dropping the subsequently unused passed wait-wound lock 'ticket'.
Patchwork: https://patchwork.freedesktop.org/patch/723564/ [rob: fixup compile errors, replace lockdep splat with somethin
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel represents a critical deadlock condition within the display subsystem's memory management logic, specifically affecting the Qualcomm Snapdragon X1 platform. This issue manifests during virtual memory reclaim operations when the kernel's kswapd daemon attempts to free memory pages while concurrently managing graphics memory reservations through the msm (mobile scenario module) driver. The root cause stems from improper lock ordering that creates a circular dependency between the filesystem reclaim lock and the reservation wait-wound class lock, leading to a complete system hang during memory pressure scenarios.
The technical flaw occurs within the drm/msm subsystem where the msm_gem_shrinker_scan function attempts to acquire locks in an incorrect sequence that violates the kernel's locking hierarchy. When kswapd0 holds the fs_reclaim lock and subsequently calls into the MSM shrinker code path, it triggers a call to dma_resv_lock which attempts to acquire the reservation_ww_class_acquire lock. This creates a circular dependency where the same thread holds fs_reclaim while trying to acquire reservation_ww_class_mutex, which itself depends on fs_reclaim, resulting in an irrecoverable deadlock state. The kernel's lock validator detects this condition and generates a detailed backtrace showing the chain of dependencies that leads to the deadlock.
This vulnerability directly impacts system stability and resource management during high memory pressure conditions, particularly affecting devices running Snapdragon X1 processors where graphics memory management is intensive. The operational impact includes complete system freezes, unresponsiveness of the graphical subsystem, and potential denial of service scenarios when the kernel cannot properly reclaim memory resources. The issue is particularly severe because it occurs within the core memory management pathways that are invoked automatically during low memory conditions, making it difficult to predict or avoid.
The mitigation strategy involves replacing the problematic dma_resv_lock() call with dma_resv_trylock() to eliminate the blocking behavior that causes the circular dependency. This change removes the need for the wait-wound lock 'ticket' parameter which was previously passed but subsequently unused, reducing complexity in the locking mechanism. The fix aligns with best practices for lock ordering and prevents the deadlock by avoiding the acquisition of locks in problematic sequences. This approach follows established patterns in kernel development where trylock operations are preferred over blocking locks in scenarios where circular dependencies might occur. The solution addresses the vulnerability at its root cause level, ensuring that memory management operations can proceed without creating conditions that lead to system-wide lock contention and potential crashes.
This vulnerability maps to CWE-367: Time-of-Check Time-of-Use (TOCTOU) and CWE-121: Stack-based Buffer Overflow, though the specific manifestation is a deadlock condition rather than buffer corruption. From an ATT&CK perspective, this represents a system stability compromise that could be leveraged by adversaries to create denial of service conditions or potentially escalate privileges through system resource exhaustion attacks. The fix demonstrates proper lock management practices and aligns with kernel security hardening guidelines for preventing concurrent access violations in device drivers.