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charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm100001.china.huawei.com (7.185.36.93) X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: D4F084001B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: rt1g3u4j4cm3iohtzxqzq5kkubz36i68 X-HE-Tag: 1692349295-185439 X-HE-Meta: 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 HoOqQTHP npcy8Ay+aJVcCXPLMUz99I4gZJ3bI1hqh6rO4odTzxo5vkhiDO+vzlxky6+M4H3jl+DX2nQ4e70qCCo+TnGcrDFAgp3ruZrL9jeizO+D2/Sc1LqZPh9DT8LDCx07ZG7AcETaSEXsWGz4A+BSdN2cS5z2s6XfGiobg9KBSKVrvUElXhHI3XtKSgEEMf/2kbjOokLAqkxZbnSWJZq9sNy4l9mEIdl8yS1vzdaKIUOtUcXjH8MmMXyJ5S3zGQQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/8/18 16:17, Tong Tiangen wrote: > 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(), we will not modify the tasklist, but only perform > read traversal. Therefore, we can use rcu lock instead of spin lock > tasklist_lock, from this, we can break the softlock chain above. > > The same logic can also be applied to: > - collect_procs_file() > - collect_procs_fsdax() > - collect_procs_ksm() > - find_early_kill_thread() > > Signed-off-by: Tong Tiangen > --- > v2: > - 1. Modify the title description. > - 2. Optimize the implementation of find_early_kill_thread() without > functional changes. > --- Those changes are fine to me， please fix the comment mentioned by Noaoya. > mm/ksm.c | 4 ++-- > mm/memory-failure.c | 33 +++++++++++++++++++-------------- > 2 files changed, 21 insertions(+), 16 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index 6b7b8928fb96..dcbc0c7f68e7 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -2919,7 +2919,7 @@ 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; > @@ -2938,7 +2938,7 @@ void collect_procs_ksm(struct page *page, struct list_head *to_kill, > } > } > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > anon_vma_unlock_read(av); > } > } > diff --git a/mm/memory-failure.c b/mm/memory-failure.c > index 7b01fffe7a79..4f3081f47798 100644 > --- a/mm/memory-failure.c > +++ b/mm/memory-failure.c > @@ -546,24 +546,29 @@ static void kill_procs(struct list_head *to_kill, int forcekill, bool fail, > * Find a dedicated thread which is supposed to handle SIGBUS(BUS_MCEERR_AO) > * on behalf of the thread group. Return task_struct of the (first found) > * dedicated thread if found, and return NULL otherwise. > - * > - * We already hold read_lock(&tasklist_lock) in the caller, so we don't > - * have to call rcu_read_lock/unlock() in this function. > */ > static struct task_struct *find_early_kill_thread(struct task_struct *tsk) > { > struct task_struct *t; > + bool found = false; > > + rcu_read_lock(); > for_each_thread(tsk, t) { > if (t->flags & PF_MCE_PROCESS) { > - if (t->flags & PF_MCE_EARLY) > - return t; > + if (t->flags & PF_MCE_EARLY) { > + found = true; > + break; > + } > } else { > - if (sysctl_memory_failure_early_kill) > - return t; > + if (sysctl_memory_failure_early_kill) { > + found = true; > + break; > + } > } > } > - return NULL; > + rcu_read_unlock(); > + > + return found ? t : NULL; > } > > /* > @@ -609,7 +614,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill, > return; > > pgoff = page_to_pgoff(page); > - read_lock(&tasklist_lock); > + rcu_read_lock(); > for_each_process(tsk) { > struct anon_vma_chain *vmac; > struct task_struct *t = task_early_kill(tsk, force_early); > @@ -626,7 +631,7 @@ static void collect_procs_anon(struct page *page, struct list_head *to_kill, > add_to_kill_anon_file(t, page, vma, to_kill); > } > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > anon_vma_unlock_read(av); > } > > @@ -642,7 +647,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill, > pgoff_t pgoff; > > i_mmap_lock_read(mapping); > - read_lock(&tasklist_lock); > + rcu_read_lock(); > pgoff = page_to_pgoff(page); > for_each_process(tsk) { > struct task_struct *t = task_early_kill(tsk, force_early); > @@ -662,7 +667,7 @@ static void collect_procs_file(struct page *page, struct list_head *to_kill, > add_to_kill_anon_file(t, page, vma, to_kill); > } > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > i_mmap_unlock_read(mapping); > } > > @@ -685,7 +690,7 @@ static void collect_procs_fsdax(struct page *page, > struct task_struct *tsk; > > i_mmap_lock_read(mapping); > - read_lock(&tasklist_lock); > + rcu_read_lock(); > for_each_process(tsk) { > struct task_struct *t = task_early_kill(tsk, true); > > @@ -696,7 +701,7 @@ static void collect_procs_fsdax(struct page *page, > add_to_kill_fsdax(t, page, vma, to_kill, pgoff); > } > } > - read_unlock(&tasklist_lock); > + rcu_read_unlock(); > i_mmap_unlock_read(mapping); > } > #endif /* CONFIG_FS_DAX */