[PATCH 0/4] Unblocked by fake_signal_wake_up then real signal

From: NIIBE Yutaka
Date: Mon Mar 19 2018 - 23:17:00 EST


Hello,

Background:
I tried to fix my own problem in suspend-to-ram with USB devices (some
device doesn't work well after suspend/resume). I know it's common
problems. Well, while I identified some problems of USB devices and
drivers, I did try my best. I fixed a USB device implementation of
mine. Then, I also located and fixed bugs in a USB user space driver
which I maintain.

Now, I think I found a kernel problem. After suspend/resume, in my
USB user space driver, a task sends a signal to another task, then,
pselect is unblocked by the signal. In this situation, a signal
handler is called correctly, but it seems that the pselect is
restarted. Expected behavior is unblocked pselect returning -EINTR.

Looking the code, my theory is:
It is a fake signal by suspend which unblocks pselect to be frozen,
and after resume, real signal is sent. When both of signals are
handled in a single call of exit_to_usermode_loop, by two calls of
do_signal, firstly for fake signal and secondly for real signal, the
system call is restarted wrongly, where it should return -EINTR.

Here is a patch series of mine for x86. I'd suggest architecture
maintainers to do similar if an architecture supports suspend/resume.

NIIBE Yutaka (4):
signal/x86: Factor out nosig handling.
signal/x86: do_signal: syscall restart should be done only once.
signal/x86: Move nosig handling at the end of exit_to_usermode_loop.
signal/x86: Move restore_saved_sigmask().

arch/x86/entry/common.c | 6 +++++-
arch/x86/include/asm/signal.h | 3 ++-
arch/x86/kernel/signal.c | 22 ++++++++++++++--------
3 files changed, 21 insertions(+), 10 deletions(-)

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2.11.0