acquire/release_in_xmit() work as bit lock in rds_send_xmit(), so they
are expected to ensure acquire/release memory ordering semantics.
However, test_and_set_bit/clear_bit() don't imply such semantics, on
top of this, following smp_mb__after_atomic() does not guarantee release
ordering (memory barrier actually should be placed before clear_bit()).
Instead, we use clear_bit_unlock/test_and_set_bit_lock() here.
Signed-off-by: Yewon Choi <[email protected]>
---
net/rds/send.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/net/rds/send.c b/net/rds/send.c
index 5e57a1581dc6..8f38009721b7 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -103,13 +103,12 @@ EXPORT_SYMBOL_GPL(rds_send_path_reset);
static int acquire_in_xmit(struct rds_conn_path *cp)
{
- return test_and_set_bit(RDS_IN_XMIT, &cp->cp_flags) == 0;
+ return test_and_set_bit_lock(RDS_IN_XMIT, &cp->cp_flags) == 0;
}
static void release_in_xmit(struct rds_conn_path *cp)
{
- clear_bit(RDS_IN_XMIT, &cp->cp_flags);
- smp_mb__after_atomic();
+ clear_bit_unlock(RDS_IN_XMIT, &cp->cp_flags);
/*
* We don't use wait_on_bit()/wake_up_bit() because our waking is in a
* hot path and finding waiters is very rare. We don't want to walk
--
2.43.0
On Thu, Mar 14, 2024 at 08:21:35PM +0900, Yewon Choi wrote:
> acquire/release_in_xmit() work as bit lock in rds_send_xmit(), so they
> are expected to ensure acquire/release memory ordering semantics.
> However, test_and_set_bit/clear_bit() don't imply such semantics, on
> top of this, following smp_mb__after_atomic() does not guarantee release
> ordering (memory barrier actually should be placed before clear_bit()).
>
> Instead, we use clear_bit_unlock/test_and_set_bit_lock() here.
>
> Signed-off-by: Yewon Choi <[email protected]>
Missing "Fixes" tag for the patch addressed to the "net" tree.
Thanks,
Michal
On Thu, 2024-03-14 at 12:51 +0100, Michal Kubiak wrote:
> On Thu, Mar 14, 2024 at 08:21:35PM +0900, Yewon Choi wrote:
> > acquire/release_in_xmit() work as bit lock in rds_send_xmit(), so
> > they
> > are expected to ensure acquire/release memory ordering semantics.
> > However, test_and_set_bit/clear_bit() don't imply such semantics,
> > on
> > top of this, following smp_mb__after_atomic() does not guarantee
> > release
> > ordering (memory barrier actually should be placed before
> > clear_bit()).
> >
> > Instead, we use clear_bit_unlock/test_and_set_bit_lock() here.
> >
> > Signed-off-by: Yewon Choi <[email protected]>
>
> Missing "Fixes" tag for the patch addressed to the "net" tree.
>
> Thanks,
> Michal
Yes, I think it needs:
Fixes: 1f9ecd7eacfd ("RDS: Pass rds_conn_path to rds_send_xmit()")
Since that is the last patch to modify the affected code. Other than
that I think the patch looks good. With the tag fixed, you can add my
rvb:
Reviewed-by: Allison Henderson <[email protected]>
>
On Thu, Mar 14, 2024 at 10:37:29PM +0000, Allison Henderson wrote:
> On Thu, 2024-03-14 at 12:51 +0100, Michal Kubiak wrote:
> > On Thu, Mar 14, 2024 at 08:21:35PM +0900, Yewon Choi wrote:
> > > acquire/release_in_xmit() work as bit lock in rds_send_xmit(), so
> > > they
> > > are expected to ensure acquire/release memory ordering semantics.
> > > However, test_and_set_bit/clear_bit() don't imply such semantics,
> > > on
> > > top of this, following smp_mb__after_atomic() does not guarantee
> > > release
> > > ordering (memory barrier actually should be placed before
> > > clear_bit()).
> > >
> > > Instead, we use clear_bit_unlock/test_and_set_bit_lock() here.
> > >
> > > Signed-off-by: Yewon Choi <[email protected]>
> >
> > Missing "Fixes" tag for the patch addressed to the "net" tree.
> >
Sorry for mistake, I'll correct this and send v2 patch.
> > Thanks,
> > Michal
>
> Yes, I think it needs:
>
> Fixes: 1f9ecd7eacfd ("RDS: Pass rds_conn_path to rds_send_xmit()")
>
> Since that is the last patch to modify the affected code. Other than
> that I think the patch looks good. With the tag fixed, you can add my
> rvb:
>
Also, test_and_set_bit/clear_bit() was first introduced in
commit 0f4b1c7e89e6. I think this can be added, too:
Fixes: 0f4b1c7e89e6 ("rds: fix rds_send_xmit() serialization")
> Reviewed-by: Allison Henderson <[email protected]>
> >
>
Thank you for the reviewing.
Sincerely,
Yewon Choi