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Fri, 28 Aug 2026 09:18:02 +0000 X-Mizu-Trace-ID: 3ee0ae8b69a5b7fd X-Migadu-Flow: FLOW_OUT From: Ye Liu To: Andrew Morton , Uladzislau Rezki Cc: Ye Liu , Dev Jain , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] mm: vmalloc: fix vmap_purge_lock livelock under memory pressure Date: Fri, 28 Aug 2026 17:17:53 +0800 Message-Id: <20260828091753.299295-1-ye.liu@linux.dev> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 59EDCA0003 X-Stat-Signature: m7p96gesq88jooemsobj5ugrozx3fswf X-HE-Tag: 1787908684-941722 X-HE-Meta: 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 7I2pwZLt zxvGvUo08HydISqC9icl/EKCUo/cTFWsiJW8Bs6OXKZP9qmRTvOanYqoAhct/F8CiEFkyCnHcQtXONdBm0sBu3aLgchzUKpTdOvJJmfMxnWJRkSuUplNx1UsJjvBoh3sMQx6FFOy60JIWjf5eVfbKP1PgAZqhWH3KT/uq1TAflj6UpFRLMVqAiqgkPGz9Makd8eGdydO2tjKmDn0dx5DDFRK5j0Q8ghtfu41bqZgXh6Psic4UPyTsBgErJhvRCYuW467nqWELvcrpFdSMRPHLAZVgXdLVOI+szunq6Pbb7wtWRhJLz/JQ94ncQtkMfhsffCfulakg5DZBZ46yn4SBGoitkgCZfMh6+la/p+bBe5Xv0AWgv+uf3xYsJeMtWxqZ+fdg Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Ye Liu The vmap_purge_lock mutex can be held for an extended period by __purge_vmap_area_lazy() which calls flush_work() to wait for purge_vmap_node workers while holding the lock. Under memory pressure, those workers may themselves be blocked in direct reclaim trying to acquire the same lock via the vmap_node_shrink_scan() shrinker callback, creating a circular dependency that deadlocks the entire system. Two places acquire vmap_purge_lock from paths that can be reached during direct reclaim: 1. vmap_node_shrink_scan(): replace blocking guard(mutex) with mutex_trylock(). This is a shrinker that only decays the vmap pool and returns SHRINK_STOP without freeing memory; skipping a decay cycle when the lock is contended is harmless and prevents tasks from piling up on the mutex in the direct reclaim path. 2. reclaim_and_purge_vmap_areas(): replace mutex_lock() with mutex_trylock(). This is called from the vmalloc allocation overflow path; if trylock fails, another thread is already purging and the allocator's retry will find freed space. The notifier chain provides a fallback if the retry still fails. Both trylock failures break the circular dependency: the lock holder's flush_work() can complete because workers are no longer blocked on vmap_purge_lock in the direct reclaim path. Fixes: 7679ba6b36db ("mm: vmalloc: add a shrinker to drain vmap pools") Suggested-by: Uladzislau Rezki Suggested-by: Dev Jain Signed-off-by: Ye Liu --- v2: - Use mutex_trylock instead of mutex_lock to acquire vmap_purge_lock, as suggested by Uladzislau Rezki and Dev Jain. - Link: https://lore.kernel.org/all/20260824095020.1225189-1-ye.liu@linux.dev/ mm/vmalloc.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index bea9f76ed7e7..e5c68b795a3e 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2440,7 +2440,8 @@ static bool __purge_vmap_area_lazy(unsigned long start, unsigned long end, static void reclaim_and_purge_vmap_areas(void) { - mutex_lock(&vmap_purge_lock); + if (!mutex_trylock(&vmap_purge_lock)) + return; purge_fragmented_blocks_allcpus(); __purge_vmap_area_lazy(ULONG_MAX, 0, true); mutex_unlock(&vmap_purge_lock); @@ -5519,10 +5520,20 @@ vmap_node_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { struct vmap_node *vn; - guard(mutex)(&vmap_purge_lock); + /* + * This shrinker is invoked from direct reclaim where memory + * pressure is already high. Blocking on vmap_purge_lock here + * can deadlock the system: the lock holder may be blocked in + * flush_work() waiting for a worker that is stuck in this same + * reclaim path trying to acquire the same lock. Use trylock + * to avoid this; skipping a pool decay cycle is harmless. + */ + if (!mutex_trylock(&vmap_purge_lock)) + return SHRINK_STOP; for_each_vmap_node(vn) decay_va_pool_node(vn, true); + mutex_unlock(&vmap_purge_lock); return SHRINK_STOP; } -- 2.25.1