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Subject[PATCH v2 0/4] Fix no signal delivery at do_signal
Date
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 woken up by the signal. In this situation, a signal
handler is called correctly, but it seems that the pselect is
restarted. Expected behavior is woken pselect returning -EINTR.

Looking the code, my theory is:
It is a fake signal by suspend which wakes up 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.

I found that, in arch/arm, it does differently. When it finds no
signal delivery at do_signal, it restarts the system call soon,
breaking the loop. This approach also works.

Changes from v1:
* Title change of cover leter
* Avoid User Mode Linux breakage
* Only call nosig_restart_syscall when really needed
* Add 'unlikely'.

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

arch/x86/entry/common.c | 6 +++++-
arch/x86/include/asm/signal.h | 5 ++++-
arch/x86/kernel/signal.c | 22 ++++++++++++++--------
3 files changed, 23 insertions(+), 10 deletions(-)

--
2.11.0

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