LOCKDEP NMI warning highlighted potential deadlock of hashtab in NMI
context:
[ 74.828971] ================================
[ 74.828972] WARNING: inconsistent lock state
[ 74.828973] 5.9.0-rc8+ #275 Not tainted
[ 74.828974] --------------------------------
[ 74.828975] inconsistent {INITIAL USE} -> {IN-NMI} usage.
[ 74.828976] taskset/1174 [HC2[2]:SC0[0]:HE0:SE1] takes:
[...]
[ 74.828999] Possible unsafe locking scenario:
[ 74.828999]
[ 74.829000] CPU0
[ 74.829001] ----
[ 74.829001] lock(&htab->buckets[i].raw_lock);
[ 74.829003] <Interrupt>
[ 74.829004] lock(&htab->buckets[i].raw_lock);
Please refer to patch 1/2 for full trace.
This warning is a false alert, as "INITIAL USE" and "IN-NMI" in the tests
are from different hashtab. On the other hand, in theory, it is possible
to deadlock when a hashtab is access from both non-NMI and NMI context.
Patch 1/2 fixes this false alert by assigning separate lockdep class to
each hashtab. Patch 2/2 introduces map_locked counters, which is similar to
bpf_prog_active counter, to avoid hashtab deadlock in NMI context.
Song Liu (2):
bpf: use separate lockdep class for each hashtab
bpf: Avoid hashtab deadlock with map_locked
kernel/bpf/hashtab.c | 126 +++++++++++++++++++++++++++++++------------
1 file changed, 92 insertions(+), 34 deletions(-)
--
2.24.1
