nanosleep() syscall waking up with bus error?

I'm looking at a core dump from an embedded MIPS Linux app. GDB is reporting SIGBUS, and the thread handling the signal appears to be sat in a syscall for nanosleep - the higher level code basically called sleep(verylongtime); Assuming another process didn't send that signal to the app, what would cause this thread to be woken up like this? Has something inside the kernel generated the b开发者_开发问答us error? Could it have been caused by another thread that blocks such signals? (please excuse any naivety here, I'm not too knowledgeable about signals). Thanks.

If si_pid is set to an address, this means your SIGBUS was raised by a fault in the program. Usually this happens when the kernel tries to page in some program text, but encounters an IO error. Stack overflows can also trigger this.

You see si_pid set to an address because si_pid is part of a union, and is aliased with si_address. In particular, si_pid is only valid if si_code == SI_USER. You may be able to get more information from the si_code member:

   The following values can be placed in si_code for a SIGBUS signal:

       BUS_ADRALN     invalid address alignment

       BUS_ADRERR     nonexistent physical address

       BUS_OBJERR     object-specific hardware error

       BUS_MCEERR_AR (since Linux 2.6.32)
                      Hardware memory error consumed on a machine check; action required.

       BUS_MCEERR_AO (since Linux 2.6.32)
                      Hardware memory error detected in process but not consumed; action optional.

Note that it is not possible to block kernel-originated SIGBUS signals - if you try to do so, your program will be terminated anyway.

I suspect your debugger may be a bit confused as to the origin of the SIGBUS signal here; it may be attributing it to the wrong thread. You may want to examine the other threads of your process to see if they're doing anything odd. Alternately, you may have encountered an IO error when returning from the nanosleep and paging in the page of code at the return address.