Revision f37755490fe9bf76f6ba1d8c6591745d3574a6a6 authored by Steven Rostedt (Red Hat) on 15 February 2016, 17:36:14 UTC, committed by Steven Rostedt on 15 February 2016, 18:04:46 UTC
The tracepoint infrastructure uses RCU sched protection to enable and
disable tracepoints safely. There are some instances where tracepoints are
used in infrastructure code (like kfree()) that get called after a CPU is
going offline, and perhaps when it is coming back online but hasn't been
registered yet.
This can probuce the following warning:
[ INFO: suspicious RCU usage. ]
4.4.0-00006-g0fe53e8-dirty #34 Tainted: G S
-------------------------------
include/trace/events/kmem.h:141 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
RCU used illegally from offline CPU! rcu_scheduler_active = 1, debug_locks = 1
no locks held by swapper/8/0.
stack backtrace:
CPU: 8 PID: 0 Comm: swapper/8 Tainted: G S 4.4.0-00006-g0fe53e8-dirty #34
Call Trace:
[c0000005b76c78d0] [c0000000008b9540] .dump_stack+0x98/0xd4 (unreliable)
[c0000005b76c7950] [c00000000010c898] .lockdep_rcu_suspicious+0x108/0x170
[c0000005b76c79e0] [c00000000029adc0] .kfree+0x390/0x440
[c0000005b76c7a80] [c000000000055f74] .destroy_context+0x44/0x100
[c0000005b76c7b00] [c0000000000934a0] .__mmdrop+0x60/0x150
[c0000005b76c7b90] [c0000000000e3ff0] .idle_task_exit+0x130/0x140
[c0000005b76c7c20] [c000000000075804] .pseries_mach_cpu_die+0x64/0x310
[c0000005b76c7cd0] [c000000000043e7c] .cpu_die+0x3c/0x60
[c0000005b76c7d40] [c0000000000188d8] .arch_cpu_idle_dead+0x28/0x40
[c0000005b76c7db0] [c000000000101e6c] .cpu_startup_entry+0x50c/0x560
[c0000005b76c7ed0] [c000000000043bd8] .start_secondary+0x328/0x360
[c0000005b76c7f90] [c000000000008a6c] start_secondary_prolog+0x10/0x14
This warning is not a false positive either. RCU is not protecting code that
is being executed while the CPU is offline.
Instead of playing "whack-a-mole(TM)" and adding conditional statements to
the tracepoints we find that are used in this instance, simply add a
cpu_online() test to the tracepoint code where the tracepoint will be
ignored if the CPU is offline.
Use of raw_smp_processor_id() is fine, as there should never be a case where
the tracepoint code goes from running on a CPU that is online and suddenly
gets migrated to a CPU that is offline.
Link: http://lkml.kernel.org/r/1455387773-4245-1-git-send-email-kda@linux-powerpc.org
Reported-by: Denis Kirjanov <kda@linux-powerpc.org>
Fixes: 97e1c18e8d17b ("tracing: Kernel Tracepoints")
Cc: stable@vger.kernel.org # v2.6.28+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
1 parent 18558ca
ecryptfs.txt
eCryptfs: A stacked cryptographic filesystem for Linux
eCryptfs is free software. Please see the file COPYING for details.
For documentation, please see the files in the doc/ subdirectory. For
building and installation instructions please see the INSTALL file.
Maintainer: Phillip Hellewell
Lead developer: Michael A. Halcrow <mhalcrow@us.ibm.com>
Developers: Michael C. Thompson
Kent Yoder
Web Site: http://ecryptfs.sf.net
This software is currently undergoing development. Make sure to
maintain a backup copy of any data you write into eCryptfs.
eCryptfs requires the userspace tools downloadable from the
SourceForge site:
http://sourceforge.net/projects/ecryptfs/
Userspace requirements include:
- David Howells' userspace keyring headers and libraries (version
1.0 or higher), obtainable from
http://people.redhat.com/~dhowells/keyutils/
- Libgcrypt
NOTES
In the beta/experimental releases of eCryptfs, when you upgrade
eCryptfs, you should copy the files to an unencrypted location and
then copy the files back into the new eCryptfs mount to migrate the
files.
MOUNT-WIDE PASSPHRASE
Create a new directory into which eCryptfs will write its encrypted
files (i.e., /root/crypt). Then, create the mount point directory
(i.e., /mnt/crypt). Now it's time to mount eCryptfs:
mount -t ecryptfs /root/crypt /mnt/crypt
You should be prompted for a passphrase and a salt (the salt may be
blank).
Try writing a new file:
echo "Hello, World" > /mnt/crypt/hello.txt
The operation will complete. Notice that there is a new file in
/root/crypt that is at least 12288 bytes in size (depending on your
host page size). This is the encrypted underlying file for what you
just wrote. To test reading, from start to finish, you need to clear
the user session keyring:
keyctl clear @u
Then umount /mnt/crypt and mount again per the instructions given
above.
cat /mnt/crypt/hello.txt
NOTES
eCryptfs version 0.1 should only be mounted on (1) empty directories
or (2) directories containing files only created by eCryptfs. If you
mount a directory that has pre-existing files not created by eCryptfs,
then behavior is undefined. Do not run eCryptfs in higher verbosity
levels unless you are doing so for the sole purpose of debugging or
development, since secret values will be written out to the system log
in that case.
Mike Halcrow
mhalcrow@us.ibm.com
Computing file changes ...
