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perf, hw_breakpoint, kgdb: Do not take mutex for kernel debugger

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This patch fixes the regression in functionality where the
kernel debugger and the perf API do not nicely share hw
breakpoint reservations.

The kernel debugger cannot use any mutex_lock() calls because it
can start the kernel running from an invalid context.

A mutex free version of the reservation API needed to get
created for the kernel debugger to safely update hw breakpoint
reservations.

The possibility for a breakpoint reservation to be concurrently
processed at the time that kgdb interrupts the system is
improbable. Should this corner case occur the end user is
warned, and the kernel debugger will prohibit updating the
hardware breakpoint reservations.

Any time the kernel debugger reserves a hardware breakpoint it
will be a system wide reservation.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: kgdb-bugreport@lists.sourceforge.net
Cc: K.Prasad <prasad@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: torvalds@linux-foundation.org
LKML-Reference: <1264719883-7285-3-git-send-email-jason.wessel@windriver.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Jason Wessel
2010-01-28 17:04:43 -06:00
committed by Ingo Molnar
parent cc0967490c
commit 5352ae638e
3 changed files with 95 additions and 10 deletions
Download Patch File Download Diff File Expand all files Collapse all files

51
arch/x86/kernel/kgdb.c
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@@ -239,6 +239,49 @@ static void kgdb_correct_hw_break(void)
hw_breakpoint_restore();
}
static int hw_break_reserve_slot(int breakno)
{
int cpu;
int cnt = 0;
struct perf_event **pevent;
for_each_online_cpu(cpu) {
cnt++;
pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
if (dbg_reserve_bp_slot(*pevent))
goto fail;
}
return 0;
fail:
for_each_online_cpu(cpu) {
cnt--;
if (!cnt)
break;
pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
dbg_release_bp_slot(*pevent);
}
return -1;
}
static int hw_break_release_slot(int breakno)
{
struct perf_event **pevent;
int cpu;
for_each_online_cpu(cpu) {
pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
if (dbg_release_bp_slot(*pevent))
/*
* The debugger is responisble for handing the retry on
* remove failure.
*/
return -1;
}
return 0;
}
static int
kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
{
@@ -250,6 +293,10 @@ kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
if (i == 4)
return -1;
if (hw_break_release_slot(i)) {
printk(KERN_ERR "Cannot remove hw breakpoint at %lx\n", addr);
return -1;
}
breakinfo[i].enabled = 0;
return 0;
@@ -316,6 +363,10 @@ kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
return -1;
}
breakinfo[i].addr = addr;
if (hw_break_reserve_slot(i)) {
breakinfo[i].addr = 0;
return -1;
}
breakinfo[i].enabled = 1;
return 0;