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nexthop: Fix splat with CONFIG_DEBUG_PREEMPT=y
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Locally generated packets can increment the new nexthop statistics from
process context, resulting in the following splat [1] due to preemption
being enabled. Fix by using get_cpu_ptr() / put_cpu_ptr() which will
which take care of disabling / enabling preemption.

BUG: using smp_processor_id() in preemptible [00000000] code: ping/949
caller is nexthop_select_path+0xcf8/0x1e30
CPU: 12 PID: 949 Comm: ping Not tainted 6.8.0-rc7-custom-gcb450f605fae #11
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xbd/0xe0
 check_preemption_disabled+0xce/0xe0
 nexthop_select_path+0xcf8/0x1e30
 fib_select_multipath+0x865/0x18b0
 fib_select_path+0x311/0x1160
 ip_route_output_key_hash_rcu+0xe54/0x2720
 ip_route_output_key_hash+0x193/0x380
 ip_route_output_flow+0x25/0x130
 raw_sendmsg+0xbab/0x34a0
 inet_sendmsg+0xa2/0xe0
 __sys_sendto+0x2ad/0x430
 __x64_sys_sendto+0xe5/0x1c0
 do_syscall_64+0xc5/0x1d0
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
[...]

Fixes: f4676ea ("net: nexthop: Add nexthop group entry stats")
Signed-off-by: Ido Schimmel <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
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idosch authored and kuba-moo committed Mar 12, 2024
1 parent d8a2107 commit e006858
Showing 1 changed file with 2 additions and 1 deletion.
3 changes: 2 additions & 1 deletion net/ipv4/nexthop.c
Original file line number Diff line number Diff line change
Expand Up @@ -674,10 +674,11 @@ static void nh_grp_entry_stats_inc(struct nh_grp_entry *nhge)
{
struct nh_grp_entry_stats *cpu_stats;

cpu_stats = this_cpu_ptr(nhge->stats);
cpu_stats = get_cpu_ptr(nhge->stats);
u64_stats_update_begin(&cpu_stats->syncp);
u64_stats_inc(&cpu_stats->packets);
u64_stats_update_end(&cpu_stats->syncp);
put_cpu_ptr(cpu_stats);
}

static void nh_grp_entry_stats_read(struct nh_grp_entry *nhge,
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