On 7 Oct 2019, at 15:40, Gleb Smirnoff wrote:
Author: glebius
Date: Mon Oct 7 22:40:05 2019
New Revision: 353292
URL: https://svnweb.freebsd.org/changeset/base/353292
Log:
Widen NET_EPOCH coverage.
When epoch(9) was introduced to network stack, it was basically
dropped in place of existing locking, which was mutexes and
rwlocks. For the sake of performance mutex covered areas were
as small as possible, so became epoch covered areas.
However, epoch doesn't introduce any contention, it just delays
memory reclaim. So, there is no point to minimise epoch covered
areas in sense of performance. Meanwhile entering/exiting epoch
also has non-zero CPU usage, so doing this less often is a win.
Not the least is also code maintainability. In the new paradigm
we can assume that at any stage of processing a packet, we are
inside network epoch. This makes coding both input and output
path way easier.
On output path we already enter epoch quite early - in the
ip_output(), in the ip6_output().
This patch does the same for the input path. All ISR processing,
network related callouts, other ways of packet injection to the
network stack shall be performed in net_epoch. Any leaf function
that walks network configuration now asserts epoch.
Tricky part is configuration code paths - ioctls, sysctls. They
also call into leaf functions, so some need to be changed.
This patch would introduce more epoch recursions (see EPOCH_TRACE)
than we had before. They will be cleaned up separately, as several
of them aren't trivial. Note, that unlike a lock recursion the
epoch recursion is safe and just wastes a bit of resources.
Reviewed by: gallatin, hselasky, cy, adrian, kristof
Differential Revision: https://reviews.freebsd.org/D19111
This appears to have broken vlan.
To reproduce do:
sudo ifconfig epair create
sudo ifconfig vlan create vlandev epair0a vlan 42
I see the following panic:
panic: Assertion in_epoch(net_epoch_preempt) failed at
/usr/src/sys/net/if_vlan.c:1353
cpuid = 5
time = 1570828155
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame
0xfffffe0060d894c0
vpanic() at vpanic+0x17e/frame 0xfffffe0060d89520
panic() at panic+0x43/frame 0xfffffe0060d89580
vlan_config() at vlan_config+0x599/frame 0xfffffe0060d895c0
vlan_clone_create() at vlan_clone_create+0x29b/frame 0xfffffe0060d89630
if_clone_createif() at if_clone_createif+0x4a/frame 0xfffffe0060d89680
ifioctl() at ifioctl+0x6f4/frame 0xfffffe0060d89750
kern_ioctl() at kern_ioctl+0x295/frame 0xfffffe0060d897b0
sys_ioctl() at sys_ioctl+0x15c/frame 0xfffffe0060d89880
amd64_syscall() at amd64_syscall+0x2b5/frame 0xfffffe0060d899b0
fast_syscall_common() at fast_syscall_common+0x101/frame
0xfffffe0060d899b0
--- syscall (54, FreeBSD ELF64, sys_ioctl), rip = 0x80047dc2a, rsp =
0x7fffffffe1a8, rbp = 0x7fffffffe1b0 ---
I guess that we need to enter net_epoch in vlan_clone_create(). Or
perhaps that’s something that’s generically needed and it should be
done on if_clone_createif().
Best regards,
Kristof
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