[PATCH] [PATCH] mm: disable preemption before swapcache_free

["zhaowuyun@wingtech.com" <zhaowuyun@wingtech.com>]

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From: zhaowuyun <zhaowuyun@wingtech.com>
 
issue is that there are two processes A and B, A is kworker/u16:8
normal priority, B is AudioTrack, RT priority, they are on the
same CPU 3.
 
The task A preempted by task B in the moment
after __delete_from_swap_cache(page) and before swapcache_free(swap).
 
The task B does __read_swap_cache_async in the do {} while loop, it
will never find the page from swapper_space because the page is removed
by the task A, and it will never sucessfully in swapcache_prepare because
the entry is EEXIST.
 
The task B then stuck in the loop infinitely because it is a RT task,
no one can preempt it.
 
so need to disable preemption until the swapcache_free executed.
 
TASK A:
=====================================================
Process: kworker/u16:8, cpu: 3 pid: 20289 start: 0xffffffc0385f8e00
=====================================================
    Task name: kworker/u16:8 pid: 20289 cpu: 3 start: ffffffc0385f8e00
    state: 0x0 exit_state: 0x0 stack base: 0xffffffc012ba0000 Prio: 120
    Stack:
    [<ffffff80bca861a4>] __switch_to+0x90
    [<ffffff80bd83eddc>] __schedule+0x29c
    [<ffffff80bd83f600>] preempt_schedule_common+0x24
    [<ffffff80bd83f63c>] preempt_schedule.part.169+0x1c
    [<ffffff80bd83f664>] preempt_schedule+0x20
    [<ffffff80bd84396c>] _raw_spin_unlock_irqrestore+0x40
    [<ffffff80bcbc4710>] __remove_mapping+0x174
    [<ffffff80bcbc7698>] shrink_page_list+0x894
    [<ffffff80bcbc7d7c>] reclaim_pages_from_list+0xc8
    [<ffffff80bcc7b910>] reclaim_pte_range+0x158
    [<ffffff80bcbf45d4>] walk_pgd_range+0xd4
    [<ffffff80bcbf476c>] walk_page_range+0x74
    [<ffffff80bcc7cd64>] reclaim_task_anon+0xdc
    [<ffffff80bcc0a4c4>] swap_fn+0x1b8
    [<ffffff80bcac2e88>] process_one_work+0x168
    [<ffffff80bcac33a0>] worker_thread+0x224
    [<ffffff80bcac9864>] kthread+0xe0
    [<ffffff80bca836e0>] ret_from_fork+0x10
 
TASK B:
[535478.724249] CPU: 3 PID: 4645 Comm: AudioTrack Tainted: GF    UD W  O 4.9.82-perf+ #1
[535478.724385] Hardware name: Qualcomm Technologies, Inc. SDM450 PMI632 MTP S3 (DT)
[535478.724479] task: ffffffc026ce2a00 task.stack: ffffffc012e14000
[535478.724537] PC is at __read_swap_cache_async+0x154/0x25c
[535478.724630] LR is at __read_swap_cache_async+0x9c/0x25c
...
[535478.735546] [<ffffff80bcbf9970>] __read_swap_cache_async+0x154/0x25c
[535478.735599] [<ffffff80bcbf9a98>] read_swap_cache_async+0x20/0x54
[535478.735697] [<ffffff80bcbf9b24>] swapin_readahead+0x58/0x218
[535478.735797] [<ffffff80bcbe5240>] do_swap_page+0x3c4/0x4d0
[535478.735850] [<ffffff80bcbe6bf8>] handle_mm_fault+0x364/0xba4
[535478.735949] [<ffffff80bca9b5a8>] do_page_fault+0x2a0/0x38c
[535478.736003] [<ffffff80bca9b79c>] do_translation_fault+0x40/0x48
[535478.736100] [<ffffff80bca81340>] do_mem_abort+0x50/0xc8
 
Change-Id: I36d9df7ccff77c589b7157225410269c675a8504
Signed-off-by: zhaowuyun <zhaowuyun@wingtech.com>
---
mm/vmscan.c | 9 +++++++++
1 file changed, 9 insertions(+)
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2740973..acede002 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -674,6 +674,12 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
BUG_ON(!PageLocked(page));
BUG_ON(mapping != page_mapping(page));
+ /*
+ * preemption must be disabled to protect current task preempted before
+ * swapcache_free(swap) invoked by the task which do the
+ * __read_swap_cache_async job on the same page
+ */
+ preempt_disable();
spin_lock_irqsave(&mapping->tree_lock, flags);
/*
* The non racy check for a busy page.
@@ -714,6 +720,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
__delete_from_swap_cache(page);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
swapcache_free(swap);
+ preempt_enable();
} else {
void (*freepage)(struct page *);
void *shadow = NULL;
@@ -740,6 +747,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
shadow = workingset_eviction(mapping, page);
__delete_from_page_cache(page, shadow);
spin_unlock_irqrestore(&mapping->tree_lock, flags);
+ preempt_enable();
if (freepage != NULL)
freepage(page);
@@ -749,6 +757,7 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
cannot_free:
spin_unlock_irqrestore(&mapping->tree_lock, flags);
+ preempt_enable();
return 0;
}
-- 
1.9.1
 

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