PURPOSE of /tools/glibc/Regression/bz495955-RHEL5-glibc-doesn-t-use-private-futex-system
Description: Test for bz495955 ([RHEL5] glibc doesn't use private futex system)
Author: Petr Muller <pmuller@redhat.com>
Bug summary: [RHEL5] glibc doesn't use private futex system calls for pthread_mutex calls
Bugzilla link: https://bugzilla.redhat.com/show_bug.cgi?id=495955

Description:

Created an attachment (id=339722)
private mutex test case

As I understand it, RHEL 5.3 is supposed to have pulled in the change to use PTHREAD_PROCESS_PRIVATE by default with the various pthread_mutex calls.  While testing my recent requeue_pi code, I was seeing some unexpected behaviour on RHEL5.3 that didn't occur on FC10.  Specifically, regardless of what I set the mutexattr pshared attribute to, glibc would make the shared versions of the futex calls. I've written the attached testcase to illustrate.  It creates a PI mutex, and will set the pshared attribute to whatever you specify in the options, or use the OS default if you use no options.  Using strace -f you can see which futex syscalls glibc used.

Compile with:
# gcc -lrt -lpthread priv-mutex.c -o priv-mutex

Note: the ETIMEDOUT is intentional in the output below.

On Fedora Core 10 with glibc 2.9:

Default is private:
[root@elm3b160 dvhart]# strace -f 2>&1 ./priv-mutex | grep FUTEX_LOCK_PI
[pid 13433] futex(0x6015e0, FUTEX_LOCK_PI_PRIVATE, 1) = -1 ETIMEDOUT (Connection timed out)

Specifying private works:
[root@elm3b160 dvhart]# strace -f 2>&1 ./priv-mutex -p | grep FUTEX_LOCK_PI
[pid 13437] futex(0x6015e0, FUTEX_LOCK_PI_PRIVATE, 1) = -1 ETIMEDOUT (Connection timed out)

Specifying shared works:
[root@elm3b160 dvhart]# strace -f 2>&1 ./priv-mutex -s | grep FUTEX_LOCK_PI
[pid 13441] futex(0x6015e0, FUTEX_LOCK_PI, 1) = -1 ETIMEDOUT (Connection timed out)


On RHEL5.3:

Default uses shared (I expected private here):
[root@elm3c31 dvhart]# strace -f 2>&1 ./priv-mutex | grep FUTEX_LOCK_PI
[pid  9051] futex(0x6015c0, FUTEX_LOCK_PI, 1) = -1 ETIMEDOUT (Connection timed out)

Setting PTHREAD_PROCESS_PRIVATE has no effect:
[root@elm3c31 dvhart]# strace -f 2>&1 ./priv-mutex -p | grep FUTEX_LOCK_PI
[pid  9055] futex(0x6015c0, FUTEX_LOCK_PI, 1) = -1 ETIMEDOUT (Connection timed out)

Specifying shared works as expected:
[root@elm3c31 dvhart]# strace -f 2>&1 ./priv-mutex -s | grep FUTEX_LOCK_PI
[pid  9059] futex(0x6015c0, FUTEX_LOCK_PI, 1) = -1 ETIMEDOUT (Connection timed out)
