Re: [igb] netconsole triggers warning in netpoll_poll_dev

Alexander Duyck wrote:

quoted

On Sun, Apr 25, 2021 at 11:47 PM Oleksandr Natalenko
[off-list ref] wrote:

quoted

Hello.

On Fri, Apr 23, 2021 at 03:58:36PM -0700, Jakub Kicinski wrote:

quoted

On Fri, 23 Apr 2021 10:19:44 +0200 Oleksandr Natalenko wrote:

quoted

On Wed, Apr 07, 2021 at 04:06:29PM -0700, Alexander Duyck wrote:

quoted

On Wed, Apr 7, 2021 at 11:07 AM Jakub Kicinski [off-list ref] wrote:

quoted

Sure, that's simplest. I wasn't sure something is supposed to prevent
this condition or if it's okay to cover it up.

I'm pretty sure it is okay to cover it up. In this case the "budget -
1" is supposed to be the upper limit on what can be reported. I think
it was assuming an unsigned value anyway.

Another alternative would be to default clean_complete to !!budget.
Then if budget is 0 clean_complete would always return false.

So, among all the variants, which one to try? Or there was a separate
patch sent to address this?

Alex's suggestion is probably best.

I'm not aware of the fix being posted. Perhaps you could take over and
post the patch if Intel doesn't chime in?

So, IIUC, Alex suggests this:

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index a45cd2b416c8..7503d5bf168a 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -7981,7 +7981,7 @@ static int igb_poll(struct napi_struct *napi, int budget)
                                                     struct igb_q_vector,
                                                     napi);
        bool clean_complete = true;
-       int work_done = 0;
+       unsigned int work_done = 0;

 #ifdef CONFIG_IGB_DCA
        if (q_vector->adapter->flags & IGB_FLAG_DCA_ENABLED)
@@ -8008,7 +8008,7 @@ static int igb_poll(struct napi_struct *napi, int budget)
        if (likely(napi_complete_done(napi, work_done)))
                igb_ring_irq_enable(q_vector);

-       return min(work_done, budget - 1);
+       return min_t(unsigned int, work_done, budget - 1);
 }

 /**

Am I right?

Thanks.

Actually a better way to go would be to probably just initialize
"clean_complete = !!budget". With that we don't have it messing with
the interrupt enables which would probably be a better behavior.

Thanks guys for the suggestions here! Finally got some time for
this, so here is the patch I'm going to queue shortly.

From ffd24e90d688ee347ab051266bfc7fca00324a68 Mon Sep 17 00:00:00 2001
From: Jesse Brandeburg <redacted>
Date: Thu, 6 May 2021 14:41:11 -0700
Subject: [PATCH net] igb: fix netpoll exit with traffic
To: netdev,
    Oleksandr Natalenko [off-list ref]
Cc: Jakub Kicinski <kuba@kernel.org>, LKML <redacted>, "Brandeburg, Jesse" <redacted>, "Nguyen, Anthony L" <anthony.l.nguyen@intel.com>, "David S. Miller" <davem@davemloft.net>, intel-wired-lan <redacted>, Alexander Duyck <redacted>

Oleksandr brought a bug report where netpoll causes trace messages in
the log on igb.

[22038.710800] ------------[ cut here ]------------
[22038.710801] igb_poll+0x0/0x1440 [igb] exceeded budget in poll
[22038.710802] WARNING: CPU: 12 PID: 40362 at net/core/netpoll.c:155 netpoll_poll_dev+0x18a/0x1a0

After some discussion and debug from the list, it was deemed that the
right thing to do is initialize the clean_complete variable to false
when the "netpoll mode" of passing a zero budget is used.

This logic should be sane and not risky because the only time budget
should be zero on entry is netpoll.  Change includes a small refactor
of local variable assignments to clean up the look.

Fixes: 16eb8815c235 ("igb: Refactor clean_rx_irq to reduce overhead and improve performance")
Reported-by: Oleksandr Natalenko <redacted>
Suggested-by: Alexander Duyck <redacted>
Signed-off-by: Jesse Brandeburg <redacted>
---

Compile tested ONLY, but functionally it should be exactly the same for
all cases except when budget is zero on entry, which will hopefully fix
the bug.
---
 drivers/net/ethernet/intel/igb/igb_main.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 0cd37ad81b4e..b0a9bed14071 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c

@@ -7991,12 +7991,16 @@ static void igb_ring_irq_enable(struct igb_q_vector *q_vector)
  **/
 static int igb_poll(struct napi_struct *napi, int budget)
 {
-       struct igb_q_vector *q_vector = container_of(napi,
-                                                    struct igb_q_vector,
-                                                    napi);
-       bool clean_complete = true;
+       struct igb_q_vector *q_vector;
+       bool clean_complete;
        int work_done = 0;

+       /* if budget is zero, we have a special case for netconsole, so
+        * make sure to set clean_complete to false in that case.
+        */
+       clean_complete = !!budget;
+
+       q_vector = container_of(napi, struct igb_q_vector, napi);
 #ifdef CONFIG_IGB_DCA
        if (q_vector->adapter->flags & IGB_FLAG_DCA_ENABLED)
                igb_update_dca(q_vector);