| Message ID | 1461641797-9368-1-git-send-email-yang.shi@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 4/26/2016 5:39 AM, Peter Zijlstra wrote: > On Mon, Apr 25, 2016 at 08:36:37PM -0700, Yang Shi wrote: >> When kernel oops happens, lock debugging is turned off by debug_locks_off() >> in oops_enter() via calling __debug_locks_off() which set debug_locks to 0 >> via xchg(). But, calling to __debug_locks_off() to check lock debugging state >> in add_taint() called by oops_end() will always return false since xchg() >> returns the old value of debug_locks which is cleared in oops_enter() already. >> >> This prevents add_taint() from printing out lock debugging disable information >> although LOCKDEP_NOW_UNRELIABLE is passed to it. >> >> Check lock debugging state via !debug_locks to fix this. Although >> !__debug_locks_off() could do the same thing, it may look confusing. >> > What are you smoking? This is the second completely insane patch you > send this week. > > This breaks add_taint() and gains us nothing except trivialities. Who I apologize in advance, if I misunderstand the code and please ignore all the bullshit below. In my understanding, add_taint() should call that pr_warn if LOCKDEP_NOW_UNRELIABLE is passed and lock debugging is disabled. This is what the code tells me. LOCKDEP_NOW_UNRELIABLE is passed via lock_ok parameter, lock debugging is turned off by debug_locks_off() already, so it should print out something, but it doesn't since __debug_locks_off() always returns 0. So, it looks the if statement logic is broken. There are alternatives to fix it, I may pick up the not ideal one. > bloody cares about that print if you've just had an OOPS. I do agree not too many people care about that print and such information is too trivial to draw attention from people. However, it doesn't mean oops print is a perfect place to hide something wrong. I just happened to find this by checking the oops information to try to get some clue for another issue. Then I thought it is just a quick fix, why not I should do that to make kernel better. Thanks, Yang >
diff --git a/kernel/panic.c b/kernel/panic.c index 535c965..859499d 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -346,11 +346,11 @@ unsigned long get_taint(void) * @lockdep_ok: whether lock debugging is still OK. * * If something bad has gone wrong, you'll want @lockdebug_ok = false, but for - * some notewortht-but-not-corrupting cases, it can be set to true. + * some noteworthy-but-not-corrupting cases, it can be set to true. */ void add_taint(unsigned flag, enum lockdep_ok lockdep_ok) { - if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && __debug_locks_off()) + if (lockdep_ok == LOCKDEP_NOW_UNRELIABLE && !debug_locks) pr_warn("Disabling lock debugging due to kernel taint\n"); set_bit(flag, &tainted_mask);
When kernel oops happens, lock debugging is turned off by debug_locks_off() in oops_enter() via calling __debug_locks_off() which set debug_locks to 0 via xchg(). But, calling to __debug_locks_off() to check lock debugging state in add_taint() called by oops_end() will always return false since xchg() returns the old value of debug_locks which is cleared in oops_enter() already. This prevents add_taint() from printing out lock debugging disable information although LOCKDEP_NOW_UNRELIABLE is passed to it. Check lock debugging state via !debug_locks to fix this. Although !__debug_locks_off() could do the same thing, it may look confusing. Before the fix, oops output looks like: RIP [<ffffffff8119d2f8>] release_freepages+0x18/0xa0 RSP <ffff88036173fcf8> CR2: 0000000000000000 [ end trace 2e96d09e0ba6342f ] Aftere the fix, it looks like: RIP [<ffffffff8119d2f8>] release_freepages+0x18/0xa0 RSP <ffff88036173fcf8> CR2: 0000000000000000 Disabling lock debugging due to kernel taint [ end trace 2e96d09e0ba6342f ] And, fix a trivial typo in the comment of add_taint(). Signed-off-by: Yang Shi <yang.shi@linaro.org> --- kernel/panic.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.0.2