<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux.git/tools/testing/selftests, branch v3.8-rc2</title>
<subtitle>Linux kernel source tree</subtitle>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/'/>
<entry>
<title>tools/testing/selftests/kcmp/kcmp_test.c: print reason for failure in kcmp_test</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Jones</name>
<email>davej@redhat.com</email>
</author>
<published>2012-12-18T00:04:52+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=2bf1cbf1c616b4dd85a3a8a715af9c5701c16a91'/>
<id>2bf1cbf1c616b4dd85a3a8a715af9c5701c16a91</id>
<content type='text'>
I was curious why sys_kcmp wasn't working, which led me to the testcase.
It turned out I hadn't enabled CHECKPOINT_RESTORE in the kernel I was
testing.  Add a decoding of errno to the testcase to make that obvious.

Signed-off-by: Dave Jones &lt;davej@redhat.com&gt;
Acked-by: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
I was curious why sys_kcmp wasn't working, which led me to the testcase.
It turned out I hadn't enabled CHECKPOINT_RESTORE in the kernel I was
testing.  Add a decoding of errno to the testcase to make that obvious.

Signed-off-by: Dave Jones &lt;davej@redhat.com&gt;
Acked-by: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>breakpoint selftests: print failure status instead of cause make error</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:50+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=5a55f8bb2d0c4e5c05837b688ed1b2132a0ed0e7'/>
<id>5a55f8bb2d0c4e5c05837b688ed1b2132a0ed0e7</id>
<content type='text'>
In case breakpoint test exit non zero value it will cause make error.
Better way is just print the test failure status.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
In case breakpoint test exit non zero value it will cause make error.
Better way is just print the test failure status.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>kcmp selftests: print fail status instead of cause make error</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:49+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=ed8ad10c3b2fab18dd92d21afd4277a8a521ecfd'/>
<id>ed8ad10c3b2fab18dd92d21afd4277a8a521ecfd</id>
<content type='text'>
In case kcmp_test exit non zero value it will cause make error.
Better way is just print the test failure status.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Cc: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
In case kcmp_test exit non zero value it will cause make error.
Better way is just print the test failure status.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Cc: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>kcmp selftests: make run_tests fix</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:47+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=63d233673a9f6c524969e40e7012e3e461aafd32'/>
<id>63d233673a9f6c524969e40e7012e3e461aafd32</id>
<content type='text'>
make run_tests need the target is run_tests instead of run-tests
Also gcc output should be kcmp_test. Fix these two issues.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Cc: Pekka Enberg &lt;penberg@kernel.org&gt;
Cc: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
make run_tests need the target is run_tests instead of run-tests
Also gcc output should be kcmp_test. Fix these two issues.

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Cc: Pekka Enberg &lt;penberg@kernel.org&gt;
Cc: Cyrill Gorcunov &lt;gorcunov@openvz.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>mem-hotplug selftests: print failure status instead of cause make error</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:45+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=aabccae6e9e2106e67a40d65eb423163cd69d2fb'/>
<id>aabccae6e9e2106e67a40d65eb423163cd69d2fb</id>
<content type='text'>
Original behavior:
  bash-4.1$ make -C memory-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'
  ./on-off-test.sh
  make: execvp: ./on-off-test.sh: Permission denied
  make: *** [run_tests] Error 127
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'

After applying the patch:
  bash-4.1$ make -C memory-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'
  /bin/sh: ./on-off-test.sh: Permission denied
  memory-hotplug selftests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Original behavior:
  bash-4.1$ make -C memory-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'
  ./on-off-test.sh
  make: execvp: ./on-off-test.sh: Permission denied
  make: *** [run_tests] Error 127
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'

After applying the patch:
  bash-4.1$ make -C memory-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'
  /bin/sh: ./on-off-test.sh: Permission denied
  memory-hotplug selftests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/memory-hotplug'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>cpu-hotplug selftests: print failure status instead of cause make error</title>
<updated>2012-12-18T01:15:27+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:42+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=a58130ddc896e5a15e4de2bf50a1d89247118c23'/>
<id>a58130ddc896e5a15e4de2bf50a1d89247118c23</id>
<content type='text'>
Original behavior:
  bash-4.1$ make -C cpu-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'
  ./on-off-test.sh
  make: execvp: ./on-off-test.sh: Permission denied
  make: *** [run_tests] Error 127
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'

After applying the patch:
  bash-4.1$ make -C cpu-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'
  /bin/sh: ./on-off-test.sh: Permission denied
  cpu-hotplug selftests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Original behavior:
  bash-4.1$ make -C cpu-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'
  ./on-off-test.sh
  make: execvp: ./on-off-test.sh: Permission denied
  make: *** [run_tests] Error 127
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'

After applying the patch:
  bash-4.1$ make -C cpu-hotplug run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'
  /bin/sh: ./on-off-test.sh: Permission denied
  cpu-hotplug selftests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/cpu-hotplug'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>mqueue selftests: print failure status instead of cause make error</title>
<updated>2012-12-18T01:15:26+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:39+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=9ed1d90ed1e0b5788e5b9148ed70adb1a017078c'/>
<id>9ed1d90ed1e0b5788e5b9148ed70adb1a017078c</id>
<content type='text'>
Original behavior:
  bash-4.1$ make -C mqueue run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'
  ./mq_open_tests /test1
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  make: *** [run_tests] Error 1
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'

After applying the patch:
  bash-4.1$ make -C mqueue run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  mq_open_tests: [FAIL]
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  mq_perf_tests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Original behavior:
  bash-4.1$ make -C mqueue run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'
  ./mq_open_tests /test1
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  make: *** [run_tests] Error 1
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'

After applying the patch:
  bash-4.1$ make -C mqueue run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  mq_open_tests: [FAIL]
  Not running as root, but almost all tests require root in order to modify
  system settings.  Exiting.
  mq_perf_tests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/mqueue'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Reviewed-by: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>vm selftests: print failure status instead of cause make error</title>
<updated>2012-12-18T01:15:26+00:00</updated>
<author>
<name>Dave Young</name>
<email>dyoung@redhat.com</email>
</author>
<published>2012-12-18T00:04:38+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=000e06b01f7e1d615345815550306a0e0622433c'/>
<id>000e06b01f7e1d615345815550306a0e0622433c</id>
<content type='text'>
Original behavior:
  bash-4.1$ make -C vm run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'
  /bin/sh ./run_vmtests
  ./run_vmtests: line 24: /proc/sys/vm/nr_hugepages: Permission denied
  Please run this test as root
  make: *** [run_tests] Error 1
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'

After applying the patch:
  bash-4.1$ make -C vm run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'
  ./run_vmtests: line 24: /proc/sys/vm/nr_hugepages: Permission denied
  Please run this test as root
  vmtests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Cc: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Original behavior:
  bash-4.1$ make -C vm run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'
  /bin/sh ./run_vmtests
  ./run_vmtests: line 24: /proc/sys/vm/nr_hugepages: Permission denied
  Please run this test as root
  make: *** [run_tests] Error 1
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'

After applying the patch:
  bash-4.1$ make -C vm run_tests
  make: Entering directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'
  ./run_vmtests: line 24: /proc/sys/vm/nr_hugepages: Permission denied
  Please run this test as root
  vmtests: [FAIL]
  make: Leaving directory `/home/dave/git/linux-2.6/tools/testing/selftests/vm'

Signed-off-by: Dave Young &lt;dyoung@redhat.com&gt;
Cc: Pekka Enberg &lt;penberg@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>selftests: add a test program for variable huge page sizes in mmap/shmget</title>
<updated>2012-12-12T01:22:25+00:00</updated>
<author>
<name>Andi Kleen</name>
<email>ak@linux.intel.com</email>
</author>
<published>2012-12-12T00:01:36+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=fcc1f2d5dd3480214ab52e06d081d123019814ed'/>
<id>fcc1f2d5dd3480214ab52e06d081d123019814ed</id>
<content type='text'>
Also remove -Wextra because gcc-4.6 emits lots of irritating
signed/unsigned comparison warnings.

Signed-off-by: Andi Kleen &lt;ak@linux.intel.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Also remove -Wextra because gcc-4.6 emits lots of irritating
signed/unsigned comparison warnings.

Signed-off-by: Andi Kleen &lt;ak@linux.intel.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>revert "epoll: support for disabling items, and a self-test app"</title>
<updated>2012-11-09T05:41:46+00:00</updated>
<author>
<name>Andrew Morton</name>
<email>akpm@linux-foundation.org</email>
</author>
<published>2012-11-08T23:53:35+00:00</published>
<link rel='alternate' type='text/html' href='https://git.tavy.me/linux.git/commit/?id=a80a6b85b428e6ce12a8363bb1f08d44c50f3252'/>
<id>a80a6b85b428e6ce12a8363bb1f08d44c50f3252</id>
<content type='text'>
Revert commit 03a7beb55b9f ("epoll: support for disabling items, and a
self-test app") pending resolution of the issues identified by Michael
Kerrisk, copied below.

We'll revisit this for 3.8.

: I've taken a look at this patch as it currently stands in 3.7-rc1, and
: done a bit of testing. (By the way, the test program
: tools/testing/selftests/epoll/test_epoll.c does not compile...)
:
: There are one or two places where the behavior seems a little strange,
: so I have a question or two at the end of this mail. But other than
: that, I want to check my understanding so that the interface can be
: correctly documented.
:
: Just to go though my understanding, the problem is the following
: scenario in a multithreaded application:
:
: 1. Multiple threads are performing epoll_wait() operations,
:    and maintaining a user-space cache that contains information
:    corresponding to each file descriptor being monitored by
:    epoll_wait().
:
: 2. At some point, a thread wants to delete (EPOLL_CTL_DEL)
:    a file descriptor from the epoll interest list, and
:    delete the corresponding record from the user-space cache.
:
: 3. The problem with (2) is that some other thread may have
:    previously done an epoll_wait() that retrieved information
:    about the fd in question, and may be in the middle of using
:    information in the cache that relates to that fd. Thus,
:    there is a potential race.
:
: 4. The race can't solved purely in user space, because doing
:    so would require applying a mutex across the epoll_wait()
:    call, which would of course blow thread concurrency.
:
: Right?
:
: Your solution is the EPOLL_CTL_DISABLE operation. I want to
: confirm my understanding about how to use this flag, since
: the description that has accompanied the patches so far
: has been a bit sparse
:
: 0. In the scenario you're concerned about, deleting a file
:    descriptor means (safely) doing the following:
:    (a) Deleting the file descriptor from the epoll interest list
:        using EPOLL_CTL_DEL
:    (b) Deleting the corresponding record in the user-space cache
:
: 1. It's only meaningful to use this EPOLL_CTL_DISABLE in
:    conjunction with EPOLLONESHOT.
:
: 2. Using EPOLL_CTL_DISABLE without using EPOLLONESHOT in
:    conjunction is a logical error.
:
: 3. The correct way to code multithreaded applications using
:    EPOLL_CTL_DISABLE and EPOLLONESHOT is as follows:
:
:    a. All EPOLL_CTL_ADD and EPOLL_CTL_MOD operations should
:       should EPOLLONESHOT.
:
:    b. When a thread wants to delete a file descriptor, it
:       should do the following:
:
:       [1] Call epoll_ctl(EPOLL_CTL_DISABLE)
:       [2] If the return status from epoll_ctl(EPOLL_CTL_DISABLE)
:           was zero, then the file descriptor can be safely
:           deleted by the thread that made this call.
:       [3] If the epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY,
:           then the descriptor is in use. In this case, the calling
:           thread should set a flag in the user-space cache to
:           indicate that the thread that is using the descriptor
:           should perform the deletion operation.
:
: Is all of the above correct?
:
: The implementation depends on checking on whether
: (events &amp; ~EP_PRIVATE_BITS) == 0
: This replies on the fact that EPOLL_CTL_AD and EPOLL_CTL_MOD always
: set EPOLLHUP and EPOLLERR in the 'events' mask, and EPOLLONESHOT
: causes those flags (as well as all others in ~EP_PRIVATE_BITS) to be
: cleared.
:
: A corollary to the previous paragraph is that using EPOLL_CTL_DISABLE
: is only useful in conjunction with EPOLLONESHOT. However, as things
: stand, one can use EPOLL_CTL_DISABLE on a file descriptor that does
: not have EPOLLONESHOT set in 'events' This results in the following
: (slightly surprising) behavior:
:
: (a) The first call to epoll_ctl(EPOLL_CTL_DISABLE) returns 0
:     (the indicator that the file descriptor can be safely deleted).
: (b) The next call to epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY.
:
: This doesn't seem particularly useful, and in fact is probably an
: indication that the user made a logic error: they should only be using
: epoll_ctl(EPOLL_CTL_DISABLE) on a file descriptor for which
: EPOLLONESHOT was set in 'events'. If that is correct, then would it
: not make sense to return an error to user space for this case?

Cc: Michael Kerrisk &lt;mtk.manpages@gmail.com&gt;
Cc: "Paton J. Lewis" &lt;palewis@adobe.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
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<pre>
Revert commit 03a7beb55b9f ("epoll: support for disabling items, and a
self-test app") pending resolution of the issues identified by Michael
Kerrisk, copied below.

We'll revisit this for 3.8.

: I've taken a look at this patch as it currently stands in 3.7-rc1, and
: done a bit of testing. (By the way, the test program
: tools/testing/selftests/epoll/test_epoll.c does not compile...)
:
: There are one or two places where the behavior seems a little strange,
: so I have a question or two at the end of this mail. But other than
: that, I want to check my understanding so that the interface can be
: correctly documented.
:
: Just to go though my understanding, the problem is the following
: scenario in a multithreaded application:
:
: 1. Multiple threads are performing epoll_wait() operations,
:    and maintaining a user-space cache that contains information
:    corresponding to each file descriptor being monitored by
:    epoll_wait().
:
: 2. At some point, a thread wants to delete (EPOLL_CTL_DEL)
:    a file descriptor from the epoll interest list, and
:    delete the corresponding record from the user-space cache.
:
: 3. The problem with (2) is that some other thread may have
:    previously done an epoll_wait() that retrieved information
:    about the fd in question, and may be in the middle of using
:    information in the cache that relates to that fd. Thus,
:    there is a potential race.
:
: 4. The race can't solved purely in user space, because doing
:    so would require applying a mutex across the epoll_wait()
:    call, which would of course blow thread concurrency.
:
: Right?
:
: Your solution is the EPOLL_CTL_DISABLE operation. I want to
: confirm my understanding about how to use this flag, since
: the description that has accompanied the patches so far
: has been a bit sparse
:
: 0. In the scenario you're concerned about, deleting a file
:    descriptor means (safely) doing the following:
:    (a) Deleting the file descriptor from the epoll interest list
:        using EPOLL_CTL_DEL
:    (b) Deleting the corresponding record in the user-space cache
:
: 1. It's only meaningful to use this EPOLL_CTL_DISABLE in
:    conjunction with EPOLLONESHOT.
:
: 2. Using EPOLL_CTL_DISABLE without using EPOLLONESHOT in
:    conjunction is a logical error.
:
: 3. The correct way to code multithreaded applications using
:    EPOLL_CTL_DISABLE and EPOLLONESHOT is as follows:
:
:    a. All EPOLL_CTL_ADD and EPOLL_CTL_MOD operations should
:       should EPOLLONESHOT.
:
:    b. When a thread wants to delete a file descriptor, it
:       should do the following:
:
:       [1] Call epoll_ctl(EPOLL_CTL_DISABLE)
:       [2] If the return status from epoll_ctl(EPOLL_CTL_DISABLE)
:           was zero, then the file descriptor can be safely
:           deleted by the thread that made this call.
:       [3] If the epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY,
:           then the descriptor is in use. In this case, the calling
:           thread should set a flag in the user-space cache to
:           indicate that the thread that is using the descriptor
:           should perform the deletion operation.
:
: Is all of the above correct?
:
: The implementation depends on checking on whether
: (events &amp; ~EP_PRIVATE_BITS) == 0
: This replies on the fact that EPOLL_CTL_AD and EPOLL_CTL_MOD always
: set EPOLLHUP and EPOLLERR in the 'events' mask, and EPOLLONESHOT
: causes those flags (as well as all others in ~EP_PRIVATE_BITS) to be
: cleared.
:
: A corollary to the previous paragraph is that using EPOLL_CTL_DISABLE
: is only useful in conjunction with EPOLLONESHOT. However, as things
: stand, one can use EPOLL_CTL_DISABLE on a file descriptor that does
: not have EPOLLONESHOT set in 'events' This results in the following
: (slightly surprising) behavior:
:
: (a) The first call to epoll_ctl(EPOLL_CTL_DISABLE) returns 0
:     (the indicator that the file descriptor can be safely deleted).
: (b) The next call to epoll_ctl(EPOLL_CTL_DISABLE) fails with EBUSY.
:
: This doesn't seem particularly useful, and in fact is probably an
: indication that the user made a logic error: they should only be using
: epoll_ctl(EPOLL_CTL_DISABLE) on a file descriptor for which
: EPOLLONESHOT was set in 'events'. If that is correct, then would it
: not make sense to return an error to user space for this case?

Cc: Michael Kerrisk &lt;mtk.manpages@gmail.com&gt;
Cc: "Paton J. Lewis" &lt;palewis@adobe.com&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
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