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clinuxsignalsrhel

malloc inside linux signal handler cause deadlock

First of all sorry for calling malloc inside signal handler :).I too understand we should not do any time consuming task/this kind of nasty stuff inside signal handler.

But i am curious to know the reason why it is crashed ? 

 #0  0x00006e3ff2b60dce in _lll_lock_wait_private () from /lib64/libc.so.6
 #1  0x00006e3ff2aec138 in _L_lock_9164 () from /lib64/libc.so.6
 #2  0x00006e3ff2ae9a32 in malloc () from /lib64/libc.so.6
 #3  0x00006e3ff1f691ad in ?? () from ..

i got similar core reported in https://access.redhat.com/solutions/48701 .

operating system : RHEL

Solution

  • malloc() is not a function that can be safely called from a signal handler. It's not a async-signal-safe function. So, you should never call malloc() from a signal handler. You are only allowed to call a limited set of functons from a signal handler. See the man signal-safety for the list of functions you can safely call from a signal handler.

    Looking at your GDB output, it appears that while malloc() is holding a lock, you are calling malloc() again which results in a deadlock.