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Description of problem:
Bash script memory utilization continually increases if bash internal pattern matching / substitution is used.
Version-Release number of selected component (if applicable):
[root@RHEL6-TEST mkandoll]# rpm -qi bash
Name : bash Relocations: (not relocatable)
Version : 4.1.2 Vendor: Red Hat, Inc.
Release : 33.el6_7.1 Build Date: Mon 17 Aug 2015 03:51:51
Install Date: Fri 25 Mar 2016 04:26:05 PM MST Build Host: x86-027.build.eng
Group : System Environment/Shells Source RPM: bash-4.1.2-33.el6_7.1.sr
Size : 3142151 License: GPLv3+
Signature : RSA/8, Thu 20 Aug 2015 08:01:55 AM MST, Key ID 199e2f91fd431d51
Packager : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
URL : http://www.gnu.org/software/bash
Summary : The GNU Bourne Again shell
How reproducible:
Every time
Steps to Reproduce:
Reproduced using script:
[root@RHEL6-BASIC mkandoll]# cat test17.sh
#!/bin/bash
while /bin/true
do
test="something1234"
test=${test//[^a-zA-Z0-9_.]/}
done
Run script for some time using:
nohup ./test17.sh 2>&1 > /dev/null &
Watch using top.
Actual results:
Memory usage increases without bound.
Expected results:
Memory is allocated first time and saved for reuse later.
Additional info:
Reproduced on a test vm using Red Hat Enterprise Linux Server release 6.5 (Santiago) that I upgraded bash package to 33.el6_7.1. Seeing this in production servers running Red Hat Enterprise Linux Server release 6.7 (Santiago).
Testing is not possible on production servers.
For a workaround I am rewriting scripts that utilize this specific substitution to use echo piped to tr.
Fixed in RHEL7 (BZ#1172214) - "Bash made a system call to allocate memory twice for the same purpose, which caused Bash to leak memory."
Patch (really stupid bug in bash 4.0-4.2):
--- bash-4.1/subst.c 2015-04-07 10:00:00.482931289 +0900
+++ bash-4.1/subst.c 2015-04-07 10:01:28.258111134 +0900
@@ -7039,8 +7039,6 @@
ret = alloc_word_desc ();
ret->word = temp1;
- ret = alloc_word_desc ();
- ret->word = temp1;
if (temp1 && QUOTED_NULL (temp1) && (quoted & (Q_HERE_DOCUMENT|Q_DOUBLE_QUOTES)))
ret->flags |= W_QUOTED|W_HASQUOTEDNULL;
return ret;
But RHEL6 still needs the patches applied.