* Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit()
[not found] <20200813024438.13170-1-jian.w.wen@oracle.com>
@ 2020-08-13 7:31 ` Christoph Hellwig
2020-08-13 7:46 ` Jacob Wen
2020-08-13 11:40 ` peterz
0 siblings, 2 replies; 4+ messages in thread
From: Christoph Hellwig @ 2020-08-13 7:31 UTC (permalink / raw)
To: Jacob Wen; +Cc: linux-fsdevel, linux-kernel, Peter Zijlstra
On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote:
> wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb().
Sounds like the barrier should go into wake_up_bit then..
>
> Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
> ---
> fs/block_dev.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 0ae656e022fd..e74980848a2a 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1175,6 +1175,7 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
> /* tell others that we're done */
> BUG_ON(whole->bd_claiming != holder);
> whole->bd_claiming = NULL;
> + smp_mb();
> wake_up_bit(&whole->bd_claiming, 0);
> }
>
> --
> 2.17.1
>
---end quoted text---
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit()
2020-08-13 7:31 ` [PATCH] block: insert a general SMP memory barrier before wake_up_bit() Christoph Hellwig
@ 2020-08-13 7:46 ` Jacob Wen
2020-08-13 11:40 ` peterz
1 sibling, 0 replies; 4+ messages in thread
From: Jacob Wen @ 2020-08-13 7:46 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: linux-fsdevel, linux-kernel, Peter Zijlstra
On 8/13/20 3:31 PM, Christoph Hellwig wrote:
> On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote:
>> wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb().
> Sounds like the barrier should go into wake_up_bit then..
wake_up_bit() doesn't know which one to chose: smp_mb__after_atomic() or
smp_mb().
>
>> Signed-off-by: Jacob Wen <jian.w.wen@oracle.com>
>> ---
>> fs/block_dev.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index 0ae656e022fd..e74980848a2a 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -1175,6 +1175,7 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
>> /* tell others that we're done */
>> BUG_ON(whole->bd_claiming != holder);
>> whole->bd_claiming = NULL;
>> + smp_mb();
>> wake_up_bit(&whole->bd_claiming, 0);
>> }
>>
>> --
>> 2.17.1
>>
> ---end quoted text---
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit()
2020-08-13 7:31 ` [PATCH] block: insert a general SMP memory barrier before wake_up_bit() Christoph Hellwig
2020-08-13 7:46 ` Jacob Wen
@ 2020-08-13 11:40 ` peterz
2020-08-13 12:00 ` Matthew Wilcox
1 sibling, 1 reply; 4+ messages in thread
From: peterz @ 2020-08-13 11:40 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Jacob Wen, linux-fsdevel, linux-kernel
On Thu, Aug 13, 2020 at 08:31:15AM +0100, Christoph Hellwig wrote:
> On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote:
> > wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb().
>
> Sounds like the barrier should go into wake_up_bit then..
Oh, thanks for reminding me..
https://lkml.kernel.org/r/20190624165012.GH3436@hirez.programming.kicks-ass.net
I'll try and get back to that.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit()
2020-08-13 11:40 ` peterz
@ 2020-08-13 12:00 ` Matthew Wilcox
0 siblings, 0 replies; 4+ messages in thread
From: Matthew Wilcox @ 2020-08-13 12:00 UTC (permalink / raw)
To: peterz; +Cc: Christoph Hellwig, Jacob Wen, linux-fsdevel, linux-kernel
On Thu, Aug 13, 2020 at 01:40:50PM +0200, peterz@infradead.org wrote:
> On Thu, Aug 13, 2020 at 08:31:15AM +0100, Christoph Hellwig wrote:
> > On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote:
> > > wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb().
> >
> > Sounds like the barrier should go into wake_up_bit then..
>
> Oh, thanks for reminding me..
>
> https://lkml.kernel.org/r/20190624165012.GH3436@hirez.programming.kicks-ass.net
>
> I'll try and get back to that.
+++ b/drivers/bluetooth/btmtkuart.c
@@ -340,11 +340,8 @@ static int btmtkuart_recv_event(struct hci_dev *hdev, struct sk_buff *skb)
if (hdr->evt == HCI_EV_VENDOR) {
if (test_and_clear_bit(BTMTKUART_TX_WAIT_VND_EVT,
- &bdev->tx_state)) {
- /* Barrier to sync with other CPUs */
- smp_mb__after_atomic();
+ &bdev->tx_state))
wake_up_bit(&bdev->tx_state, BTMTKUART_TX_WAIT_VND_EVT);
- }
}
return 0;
It'd be nice to be able to write:
if (hdr->evt == HCI_EV_VENDOR)
test_clear_and_wake_up_bit(&bdev->tx_state,
BTMTKUART_TX_WAIT_VND_EVT);
... maybe with a better name.
^ permalink raw reply [flat|nested] 4+ messages in thread
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[not found] <20200813024438.13170-1-jian.w.wen@oracle.com>
2020-08-13 7:31 ` [PATCH] block: insert a general SMP memory barrier before wake_up_bit() Christoph Hellwig
2020-08-13 7:46 ` Jacob Wen
2020-08-13 11:40 ` peterz
2020-08-13 12:00 ` Matthew Wilcox
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