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
