diff options
| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2015-08-15 11:42:21 +0200 |
|---|---|---|
| committer | Martin Schwidefsky <schwidefsky@de.ibm.com> | 2015-10-14 14:32:13 +0200 |
| commit | db7e007fd61ca07e5f3b04cf2168531b074d318d (patch) | |
| tree | 998423a5b6cfdc90b2ce91c271fa3ba0ffc380f7 /arch/s390/kernel/entry.S | |
| parent | 0c5a69f432ba1e586ac6ae5e4311c2f1cbd051fa (diff) | |
s390/udelay: make udelay have busy loop semantics
When using systemtap it was observed that our udelay implementation is
rather suboptimal if being called from a kprobe handler installed by
systemtap.
The problem observed when a kprobe was installed on lock_acquired().
When the probe was hit the kprobe handler did call udelay, which set
up an (internal) timer and reenabled interrupts (only the clock comparator
interrupt) and waited for the interrupt.
This is an optimization to avoid that the cpu is busy looping while waiting
that enough time passes. The problem is that the interrupt handler still
does call irq_enter()/irq_exit() which then again can lead to a deadlock,
since some accounting functions may take locks as well.
If one of these locks is the same, which caused lock_acquired() to be
called, we have a nice deadlock.
This patch reworks the udelay code for the interrupts disabled case to
immediately leave the low level interrupt handler when the clock
comparator interrupt happens. That way no C code is being called and the
deadlock cannot happen anymore.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/kernel/entry.S')
| -rw-r--r-- | arch/s390/kernel/entry.S | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index d653a87d66b5..857b6526d298 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -563,6 +563,8 @@ ENTRY(io_int_handler) stmg %r8,%r9,__PT_PSW(%r11) mvc __PT_INT_CODE(12,%r11),__LC_SUBCHANNEL_ID xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) + TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ + jo .Lio_restore TRACE_IRQS_OFF xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) .Lio_loop: @@ -738,6 +740,8 @@ ENTRY(ext_int_handler) mvc __PT_INT_PARM(4,%r11),__LC_EXT_PARAMS mvc __PT_INT_PARM_LONG(8,%r11),0(%r1) xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) + TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ + jo .Lio_restore TRACE_IRQS_OFF xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) lgr %r2,%r11 # pass pointer to pt_regs |