On Wed, Jan 20, 2021 at 11:12 AM Tetsuo Handa <[email protected]> wrote: > > Since syzkaller continues various test cases until the kernel crashes, > syzkaller tends to examine more locking dependencies than normal systems. > As a result, syzbot is reporting that the fuzz testing was terminated > due to hitting upper limits lockdep can track [1] [2] [3]. > > Peter Zijlstra does not want to allow tuning these limits via kernel > config options, for such change discourages thinking. But analysis via > /proc/lockdep* did not show any obvious culprit [4] [5]. It is possible > that many hundreds of kn->active lock instances are to some degree > contributing to these problems, but there is no means to verify whether > these instances are created for protecting same callback functions. > Unless Peter provides a way to make these instances per "which callback > functions the lock instance will call (identified by something like MD5 > of string representations of callback functions which each lock instance > will protect)" than plain "serial number", I don't think that we can > verify the culprit. > > [1] > https://syzkaller.appspot.com/bug?id=3d97ba93fb3566000c1c59691ea427370d33ea1b > [2] > https://syzkaller.appspot.com/bug?id=381cb436fe60dc03d7fd2a092b46d7f09542a72a > [3] > https://syzkaller.appspot.com/bug?id=a588183ac34c1437fc0785e8f220e88282e5a29f > [4] > https://lkml.kernel.org/r/[email protected] > [5] > https://lkml.kernel.org/r/[email protected] > > Reported-by: syzbot <[email protected]> > Reported-by: syzbot <[email protected]> > Reported-by: syzbot <[email protected]> > Signed-off-by: Tetsuo Handa <[email protected]> > Acked-by: Dmitry Vyukov <[email protected]>
Thanks for your persistence! I still support this. And assessment of lockdep stats on overflow seems to confirm it's just a very large lock graph triggered by syzkaller. > --- > kernel/locking/lockdep.c | 2 +- > kernel/locking/lockdep_internals.h | 8 +++--- > lib/Kconfig.debug | 40 ++++++++++++++++++++++++++++++ > 3 files changed, 45 insertions(+), 5 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index c1418b47f625..c0553872668a 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1391,7 +1391,7 @@ static int add_lock_to_list(struct lock_class *this, > /* > * For good efficiency of modular, we use power of 2 > */ > -#define MAX_CIRCULAR_QUEUE_SIZE 4096UL > +#define MAX_CIRCULAR_QUEUE_SIZE (1UL << > CONFIG_LOCKDEP_CIRCULAR_QUEUE_BITS) > #define CQ_MASK (MAX_CIRCULAR_QUEUE_SIZE-1) > > /* > diff --git a/kernel/locking/lockdep_internals.h > b/kernel/locking/lockdep_internals.h > index de49f9e1c11b..ecb8662e7a4e 100644 > --- a/kernel/locking/lockdep_internals.h > +++ b/kernel/locking/lockdep_internals.h > @@ -99,16 +99,16 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ = > #define MAX_STACK_TRACE_ENTRIES 262144UL > #define STACK_TRACE_HASH_SIZE 8192 > #else > -#define MAX_LOCKDEP_ENTRIES 32768UL > +#define MAX_LOCKDEP_ENTRIES (1UL << CONFIG_LOCKDEP_BITS) > > -#define MAX_LOCKDEP_CHAINS_BITS 16 > +#define MAX_LOCKDEP_CHAINS_BITS CONFIG_LOCKDEP_CHAINS_BITS > > /* > * Stack-trace: tightly packed array of stack backtrace > * addresses. Protected by the hash_lock. > */ > -#define MAX_STACK_TRACE_ENTRIES 524288UL > -#define STACK_TRACE_HASH_SIZE 16384 > +#define MAX_STACK_TRACE_ENTRIES (1UL << > CONFIG_LOCKDEP_STACK_TRACE_BITS) > +#define STACK_TRACE_HASH_SIZE (1 << CONFIG_LOCKDEP_STACK_TRACE_HASH_BITS) > #endif > > /* > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 7937265ef879..4cb84b499636 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1332,6 +1332,46 @@ config LOCKDEP > config LOCKDEP_SMALL > bool > > +config LOCKDEP_BITS > + int "Bitsize for MAX_LOCKDEP_ENTRIES" > + depends on LOCKDEP && !LOCKDEP_SMALL > + range 10 30 > + default 15 > + help > + Try increasing this value if you hit "BUG: MAX_LOCKDEP_ENTRIES too > low!" message. > + > +config LOCKDEP_CHAINS_BITS > + int "Bitsize for MAX_LOCKDEP_CHAINS" > + depends on LOCKDEP && !LOCKDEP_SMALL > + range 10 30 > + default 16 > + help > + Try increasing this value if you hit "BUG: MAX_LOCKDEP_CHAINS too > low!" message. > + > +config LOCKDEP_STACK_TRACE_BITS > + int "Bitsize for MAX_STACK_TRACE_ENTRIES" > + depends on LOCKDEP && !LOCKDEP_SMALL > + range 10 30 > + default 19 > + help > + Try increasing this value if you hit "BUG: MAX_STACK_TRACE_ENTRIES > too low!" message. > + > +config LOCKDEP_STACK_TRACE_HASH_BITS > + int "Bitsize for STACK_TRACE_HASH_SIZE" > + depends on LOCKDEP && !LOCKDEP_SMALL > + range 10 30 > + default 14 > + help > + Try increasing this value if you need large MAX_STACK_TRACE_ENTRIES. > + > +config LOCKDEP_CIRCULAR_QUEUE_BITS > + int "Bitsize for elements in circular_queue struct" > + depends on LOCKDEP > + range 10 30 > + default 12 > + help > + Try increasing this value if you hit "lockdep bfs error:-1" warning > due to __cq_enqueue() failure. > + > config DEBUG_LOCKDEP > bool "Lock dependency engine debugging" > depends on DEBUG_KERNEL && LOCKDEP > -- > 2.18.4 >
