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c179ea2701
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Naveen N. Rao c179ea2701 powerpc/kprobes: Fix warnings from __this_cpu_read() on preempt kernels 
Kamalesh pointed out that we are getting the below call traces with
livepatched functions when we enable CONFIG_PREEMPT:

[  495.470721] BUG: using __this_cpu_read() in preemptible [00000000] code: cat/8394
[  495.471167] caller is is_current_kprobe_addr+0x30/0x90
[  495.471171] CPU: 4 PID: 8394 Comm: cat Tainted: G              K 4.13.0-rc7-nnr+ #95
[  495.471173] Call Trace:
[  495.471178] [c00000008fd9b960] [c0000000009f039c] dump_stack+0xec/0x160 (unreliable)
[  495.471184] [c00000008fd9b9a0] [c00000000059169c] check_preemption_disabled+0x15c/0x170
[  495.471187] [c00000008fd9ba30] [c000000000046460] is_current_kprobe_addr+0x30/0x90
[  495.471191] [c00000008fd9ba60] [c00000000004e9a0] ftrace_call+0x1c/0xb8
[  495.471195] [c00000008fd9bc30] [c000000000376fd8] seq_read+0x238/0x5c0
[  495.471199] [c00000008fd9bcd0] [c0000000003cfd78] proc_reg_read+0x88/0xd0
[  495.471203] [c00000008fd9bd00] [c00000000033e5d4] __vfs_read+0x44/0x1b0
[  495.471206] [c00000008fd9bd90] [c0000000003402ec] vfs_read+0xbc/0x1b0
[  495.471210] [c00000008fd9bde0] [c000000000342138] SyS_read+0x68/0x110
[  495.471214] [c00000008fd9be30] [c00000000000bc6c] system_call+0x58/0x6c

Commit c05b8c4474 ("powerpc/kprobes: Skip livepatch_handler() for
jprobes") introduced a helper is_current_kprobe_addr() to help determine
if the current function has been livepatched or if it has a jprobe
installed, both of which modify the NIP. This was subsequently renamed
to __is_active_jprobe().

In the case of a jprobe, kprobe_ftrace_handler() disables pre-emption
before calling into setjmp_pre_handler() which returns without disabling
pre-emption. This is done to ensure that the jprobe handler won't
disappear beneath us if the jprobe is unregistered between the
setjmp_pre_handler() and the subsequent longjmp_break_handler() called
from the jprobe handler. Due to this, we can use __this_cpu_read() in
__is_active_jprobe() with the pre-emption check as we know that
pre-emption will be disabled.

However, if this function has been livepatched, we are still doing this
check and when we do so, pre-emption won't necessarily be disabled. This
results in the call trace shown above.

Fix this by only invoking __is_active_jprobe() when pre-emption is
disabled. And since we now guard this within a pre-emption check, we can
instead use raw_cpu_read() to get the current_kprobe value skipping the
check done by __this_cpu_read().

Fixes: c05b8c4474 ("powerpc/kprobes: Skip livepatch_handler() for jprobes")
Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2017-10-04 23:42:20 +11:00
..
alpha Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-09-11 18:34:47 -07:00
arc arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
arm arm/syscalls: Optimize address limit check 2017-09-17 19:45:33 +02:00
arm64 Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-09-24 11:53:13 -07:00
blackfin Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-09-11 18:34:47 -07:00
c6x arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
cris MTD changes for 4.14: 2017-09-09 14:48:21 -07:00
frv arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
h8300 arch: define CPU_BIG_ENDIAN for all fixed big endian archs 2017-09-08 18:26:48 -07:00
hexagon Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-09-04 11:52:29 -07:00
ia64 Merge branch 'work.ipc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-09-14 17:37:26 -07:00
m32r arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
m68k Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu 2017-09-10 21:07:39 -07:00
metag arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
microblaze Merge branch 'akpm' (patches from Andrew) 2017-09-09 10:30:07 -07:00
mips pci-v4.14-fixes-2 2017-09-22 13:09:11 -10:00
mn10300 arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
nios2 nios2 update for v4.14-rc1 2017-09-15 12:47:21 -07:00
openrisc OpenRISC patches for 4.14 2017-09-13 11:52:18 -07:00
parisc parisc: Unbreak bootloader due to gcc-7 optimizations 2017-09-22 22:26:43 +02:00
powerpc powerpc/kprobes: Fix warnings from __this_cpu_read() on preempt kernels 2017-10-04 23:42:20 +11:00
s390 s390/topology: enable / disable topology dynamically 2017-09-20 13:47:55 +02:00
score
sh arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
sparc Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2017-09-11 18:34:47 -07:00
tile Merge git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile 2017-09-22 13:02:54 -10:00
um arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
unicore32
x86 Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-09-24 12:33:58 -07:00
xtensa arch: remove unused *_segments() macros/functions 2017-09-22 12:59:52 -10:00
.gitignore
Kconfig - For the randstruct plugin, enable automatic randomization of structures 2017-09-07 20:30:19 -07:00