locking/lockdep: Reduce space occupied by stack traces
Although commit 669de8bd ("kernel/workqueue: Use dynamic lockdep keys for workqueues") unregisters dynamic lockdep keys when a workqueue is destroyed, a side effect of that commit is that all stack traces associated with the lockdep key are leaked when a workqueue is destroyed. Fix this by storing each unique stack trace once. Other changes in this patch are: - Use NULL instead of { .nr_entries = 0 } to represent 'no trace'. - Store a pointer to a stack trace in struct lock_class and struct lock_list instead of storing 'nr_entries' and 'offset'. This patch avoids that the following program triggers the "BUG: MAX_STACK_TRACE_ENTRIES too low!" complaint: #include <fcntl.h> #include <unistd.h> int main() { for (;;) { int fd = open("/dev/infiniband/rdma_cm", O_RDWR); close(fd); } } Suggested-by: Peter Zijlstra <peterz@infradead.org> Reported-by: Eric Biggers <ebiggers@kernel.org> Signed-off-by: Bart Van Assche <bvanassche@acm.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <longman@redhat.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Yuyang Du <duyuyang@gmail.com> Link: https://lkml.kernel.org/r/20190722182443.216015-4-bvanassche@acm.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>
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