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From: "nicholas at nicholaswilson dot me.uk" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug nis/15819] New: Hang in getaddrinfo using NIS with setitimer
Date: Tue, 06 Aug 2013 14:26:00 -0000
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X-Bugzilla-Component: nis
X-Bugzilla-Version: 2.13
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http://sourceware.org/bugzilla/show_bug.cgi?id=15819

            Bug ID: 15819
           Summary: Hang in getaddrinfo using NIS with setitimer
           Product: glibc
           Version: 2.13
            Status: NEW
          Severity: normal
          Priority: P2
         Component: nis
          Assignee: unassigned at sourceware dot org
          Reporter: nicholas at nicholaswilson dot me.uk
                CC: kukuk at suse dot de

We call getaddrinfo inside our Xorg module. Xorg unfortunately uses setitimer
to generate recurring SIGALRM notifications, at 20ms intervals. This can cause
various calls to libc to hang.

This is a typical stack trace:

#0 0xffffe402 in __kernel_vsyscall ()
#1 0x00960e6d in poll () from /lib/tls/i686/nosegneg/libc.so.6
#2 0x0098e431 in clntudp_call () from /lib/tls/i686/nosegneg/libc.so.6
#3 0x00b49f84 in do_ypcall () from /lib/libnsl.so.1
#4 0x00b4a6c0 in yp_match () from /lib/libnsl.so.1
#5 0xf77aa351 in internal_gethostbyname2_r () from /lib/libnss_nis.so.2
#6 0x009809bb in gethostbyname2_r@@GLIBC_2.1.2 () from
/lib/tls/i686/nosegneg/libc.so.6
#7 0x0094f4ea in gaih_inet () from /lib/tls/i686/nosegneg/libc.so.6
#8 0x00952c2d in getaddrinfo () from /lib/tls/i686/nosegneg/libc.so.6

The issue is that clntudp_call retries calls to poll() with every EINTR, but
does not adjust the timeout.

See sunrpc/clnt_udp.c:L403. poll() is called repeatedly with the same timeout;
we want clntudp_call() to eventually return within utimeout seconds, but when
setitemer is using a shorter timeout, clntudp_call loops forever.

The fix is to adjust the timeout to poll each time we loop. (This is the normal
way to handle EINTR with timeouts.)

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