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https://issues.apache.org/jira/browse/MYNEWT-745?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Christopher Collins updated MYNEWT-745:
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Attachment: main.c
> Sim - deadlock involving system calls
> -------------------------------------
>
> Key: MYNEWT-745
> URL: https://issues.apache.org/jira/browse/MYNEWT-745
> Project: Mynewt
> Issue Type: Bug
> Reporter: Christopher Collins
> Fix For: v1_1_0_rel
>
> Attachments: main.c
>
>
> The problem appears to occur when a system call is interrupted by a sim
> context switch. Because a sim context switch is implemented as a signal
> handler that never returns (it calls longjmp()), the system call is left
> unfinished. In some cases, it seems the system call acquired some resources
> that it never got a chance to release, leading to deadlock on a subsequent
> system call.
> Sim has protections in place to prevent this problem from happening.
> Specifically, a context switch is triggered by delivery of a SIGURG signal,
> and SIGURG is only sent from within the SIGALARM signal handler. These
> handlers are configured such that all signals are blocked until the handlers
> complete (I am not sure how this works for the SIGURG handler, considering it
> never returns).
> My initial guess was that a pending SIGURG signal does not get delivered as
> soon as it is unblocked at the end of the SIGALARM handler. However, a
> simple test using sigpending() and sleep prove that this is not the case.
> Here is a stack trace showing a context switch in the middle of a system call:
> {noformat}
> (gdb) whe
> #0 0x0804a3bd in ctxsw_handler (sig=23)
> at kernel/os/src/arch/sim/os_arch_sim.c:150
> #1 <signal handler called>
> #2 0xf7ffdbe7 in __kernel_vsyscall ()
> #3 0x08097630 in __lll_lock_wait_private ()
> #4 0x080923b0 in __tz_convert ()
> #5 0x08091673 in localtime ()
> #6 0x0809162c in ctime ()
> #7 0x08048a5a in task1_handler (arg=0x0) at apps/slinky/src/main.c:162
> #8 0x0804a2c8 in os_arch_task_start (sf=0x8160314, rc=1)
> at kernel/os/src/arch/sim/os_arch_sim.c:88
> #9 0x0804ad90 in os_arch_frame_init ()
> at kernel/os/src/arch/sim/os_arch_stack_frame.s:98
> #10 0x0804ad90 in os_arch_frame_init ()
> at kernel/os/src/arch/sim/os_arch_stack_frame.s:98
> {noformat}
> Attached is a simple Mynewt app that can be used to replicate this issue
> (main.c).
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