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authorTong Tiangen <tongtiangen@huawei.com>2023-08-28 10:25:27 +0800
committerAndrew Morton <akpm@linux-foundation.org>2023-09-05 11:11:52 -0700
commitd256d1cd8da1cbc4615de69df71c87ce623fec2f (patch)
treeceff115f2a868c0da0028e6186f61583e2d4fc2a /mm/ksm.c
parent2562d67b1bdf91c7395b0225d60fdeb26b4bc5a0 (diff)
mm: memory-failure: use rcu lock instead of tasklist_lock when collect_procs()
We found a softlock issue in our test, analyzed the logs, and found that the relevant CPU call trace as follows: CPU0: _do_fork -> copy_process() -> write_lock_irq(&tasklist_lock) //Disable irq,waiting for //tasklist_lock CPU1: wp_page_copy() ->pte_offset_map_lock() -> spin_lock(&page->ptl); //Hold page->ptl -> ptep_clear_flush() -> flush_tlb_others() ... -> smp_call_function_many() -> arch_send_call_function_ipi_mask() -> csd_lock_wait() //Waiting for other CPUs respond //IPI CPU2: collect_procs_anon() -> read_lock(&tasklist_lock) //Hold tasklist_lock ->for_each_process(tsk) -> page_mapped_in_vma() -> page_vma_mapped_walk() -> map_pte() ->spin_lock(&page->ptl) //Waiting for page->ptl We can see that CPU1 waiting for CPU0 respond IPI,CPU0 waiting for CPU2 unlock tasklist_lock, CPU2 waiting for CPU1 unlock page->ptl. As a result, softlockup is triggered. For collect_procs_anon(), what we're doing is task list iteration, during the iteration, with the help of call_rcu(), the task_struct object is freed only after one or more grace periods elapse. the logic as follows: release_task() -> __exit_signal() -> __unhash_process() -> list_del_rcu() -> put_task_struct_rcu_user() -> call_rcu(&task->rcu, delayed_put_task_struct) delayed_put_task_struct() -> put_task_struct() -> if (refcount_sub_and_test()) __put_task_struct() -> free_task() Therefore, under the protection of the rcu lock, we can safely use get_task_struct() to ensure a safe reference to task_struct during the iteration. By removing the use of tasklist_lock in task list iteration, we can break the softlock chain above. The same logic can also be applied to: - collect_procs_file() - collect_procs_fsdax() - collect_procs_ksm() Link: https://lkml.kernel.org/r/20230828022527.241693-1-tongtiangen@huawei.com Signed-off-by: Tong Tiangen <tongtiangen@huawei.com> Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com> Cc: Kefeng Wang <wangkefeng.wang@huawei.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/ksm.c')
-rw-r--r--mm/ksm.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index 8d6aee05421d..981af9c72e7a 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2925,7 +2925,7 @@ void collect_procs_ksm(struct page *page, struct list_head *to_kill,
struct anon_vma *av = rmap_item->anon_vma;
anon_vma_lock_read(av);
- read_lock(&tasklist_lock);
+ rcu_read_lock();
for_each_process(tsk) {
struct anon_vma_chain *vmac;
unsigned long addr;
@@ -2944,7 +2944,7 @@ void collect_procs_ksm(struct page *page, struct list_head *to_kill,
}
}
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
anon_vma_unlock_read(av);
}
}