From dbf14fe201c7fcab4dac75d9a5691dc726977e0b Mon Sep 17 00:00:00 2001
From: Sonic Build Admin <sonicbld@microsoft.com>
Date: Thu, 30 Apr 2026 01:01:12 +0000
Subject: [PATCH] vpp: fix race condition causing syncd crash

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### Description of PR
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Summary:
Fixes a race condition during init_switch causing syncd crash

### Type of change

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- Fill x for your type of change.
- e.g.
- [x] Bug fix
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- [x] Bug fix
- [ ] New feature
- [ ] Refactor / cleanup
- [ ] Documentation update
- [ ] Test improvement

### Approach
#### What is the motivation for this PR?
We saw below core dump during init_switch.
```
#0  0x0000ffffb5c369d0 in vpp_ev_enqueue (ev=0xaaaabe182c50) at vpp/vppxlate/SaiVppXlate.c:397
#1  vl_api_sw_interface_event_t_handler (mp=<optimized out>) at vpp/vppxlate/SaiVppXlate.c:687
#2  0x0000ffffb5264470 in vl_msg_api_handler_no_free ()
   from /nobackup/yuega2/sonic-buildimage-cisco.202603.arctos-periodic-40135/syncd_dbg/rootfs/lib/aarch64-linux-gnu/libvlibapi.so.25.02.0
#3  0x0000ffffb5205648 in ?? ()
   from /nobackup/yuega2/sonic-buildimage-cisco.202603.arctos-periodic-40135/syncd_dbg/rootfs/lib/aarch64-linux-gnu/libvlibmemoryclient.so.25.02.0
#4  0x0000ffffb5c3cd54 in vpp_intf_events_enable_disable (enable=true) at vpp/vppxlate/SaiVppXlate.c:1839
#5  init_vpp_client () at vpp/vppxlate/SaiVppXlate.c:1704
#6  0x0000ffffb5c208bc in saivs::SwitchVpp::vpp_dp_initialize (this=this@entry=0xaaaabe17a3d0) at vpp/SwitchVppRif.cpp:468
#7  0x0000ffffb5c0508c in saivs::SwitchVpp::SwitchVpp (this=this@entry=0xaaaabe17a3d0, switch_id=switch_id@entry=141733920768, manager=..., config=...,
    warmBootState=...) at vpp/SwitchVpp.cpp:44
```
This happened during init_switch right after vpp_intf_events_enable_disable, an event came in but event_queue had not been properly initialized.
##### Work item tracking
- Microsoft ADO **(number only)**:

#### How did you do it?
Move event queue initialization before enabling events from vpp.

#### How did you verify/test it?
Run sonic-mgmt via https://github.com/sonic-net/sonic-buildimage/pull/27039
#### Any platform specific information?
vpp specific
### Documentation
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Signed-off-by: Sonic Build Admin <sonicbld@microsoft.com>
---
 vslib/vpp/vppxlate/SaiVppXlate.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/vslib/vpp/vppxlate/SaiVppXlate.c b/vslib/vpp/vppxlate/SaiVppXlate.c
index 52ed7850..eda0f52a 100644
--- a/vslib/vpp/vppxlate/SaiVppXlate.c
+++ b/vslib/vpp/vppxlate/SaiVppXlate.c
@@ -1687,6 +1687,12 @@ int init_vpp_client()
         }
         dump_interface_table(vam);
 
+        /* Initialize the event queue before enabling any VPP event source,
+         * otherwise an early sw_interface_event from VPP can be dispatched
+         * to vl_api_sw_interface_event_t_handler -> vpp_ev_enqueue while
+         * vpp_evq_p is still NULL, causing a SIGSEGV. */
+        vpp_evq_init();
+
         vpp_acl_counters_enable_disable(true);
 
         /* Enable LACP punt/xc in linux-cp */
@@ -1709,7 +1715,6 @@ int init_vpp_client()
         /* Enable BFD multihop support in VPP */
         vpp_bfd_udp_enable_multihop();
 
-        vpp_evq_init();
         vpp_client_init = 1;
         return 0;
     } else {