Commit 8b401f9ed244 ("bpf: implement bpf_send_signal() helper")
introduced bpf_send_signal() helper and Commit 8482941f0906
("bpf: Add bpf_send_signal_thread() helper") added bpf_send_signal_thread()
helper. Both helpers try to send a signel to current process or thread.
When the bpf prog, hence the helper, is called in nmi mode,
the actual sending of signal is delayed to an irq_work.
But this is still not always safe as nmi could happen
in scheduler with scheduler lock is taken, later on
the routine to send signal may tries to acquire the same
spinlock and caused a deadlock. See patch #1 for more
detailed description of the problem and how to use
task_work to solve the problem.
Patch #2 is an optimization. task_work can be set up
directly in nmi mode if CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
is true. Indeed, CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG is true
for most modern architectures.
Patch #1 is for bpf tree. Patch #2 is intended for bpf-next tree.
Yonghong Song (2):
bpf: fix bpf_send_signal()/bpf_send_signal_thread() helper in NMI mode
bpf: avoid irq_work for bpf_send_signal() if
CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
kernel/trace/bpf_trace.c | 82 ++++++++++++++++++++++++++++++++--------
1 file changed, 67 insertions(+), 15 deletions(-)
--
2.17.1
