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Re: deadlock in waitchld()


From: Roman Rakus
Subject: Re: deadlock in waitchld()
Date: Fri, 24 May 2013 15:30:05 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4

The race is in do-while loop in wait_for(). At the start of wait_for() we are blocking SIGCHLD, however echo process ends during the loop and we don't register it (don't handle SIGCHLD, which is sent). Looking at the code, there is MUST_UNBLOCK_CHLD. May it make any harm to enable it by default?

RR

On 05/24/2013 02:12 PM, Roman Rakus wrote:
I have done a bit of debugging and have some results:
The problem is that waitchld is called even if there aren't any children
running. The waitchld() is called more then once. I don't know what is
the logic behind it.

Will check, if there is any child, helps?

RR

On 05/20/2013 04:11 PM, Roman Rakus wrote:
Bash hangs in wait4() (WAITPID) if TERM signal trap handler is executed
during execution of pipeline.

RR

Reproducer:
#!/bin/bash
trap "/bin/echo trapped $$" TERM
printf '%d\n' $$
while :; do
   dd if=/dev/zero bs=1k count=128 2>&1 | cat > /dev/null
done

and bombard the bash process with TERM signals:
#!/bin/bash
while :; do
   kill -TERM $1 || break
   usleep 100000
done








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