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Message-Id: <1191745762.5602.5.camel@lappy> Date: Sun, 07 Oct 2007 10:29:22 +0200 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Ingo Molnar <mingo@...e.hu>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: lockdep: how to tell it multiple pte locks is OK? On Sat, 2007-10-06 at 23:31 -0700, Jeremy Fitzhardinge wrote: > I'm writing some code which is doing some batch processing on pte pages, > and so wants to hold multiple pte locks at once. This seems OK, but > lockdep is giving me the warning: > > ============================================= > [ INFO: possible recursive locking detected ] > 2.6.23-rc9-paravirt #1673 > --------------------------------------------- > init/1 is trying to acquire lock: > (__pte_lockptr(new)){--..}, at: [<c0102d85>] lock_pte+0x10/0x15 > > but task is already holding lock: > (__pte_lockptr(new)){--..}, at: [<c0102d85>] lock_pte+0x10/0x15 > > other info that might help us debug this: > 4 locks held by init/1: > #0: (&mm->mmap_sem){----}, at: [<c012999e>] copy_process+0xab4/0x12bf > #1: (&mm->mmap_sem/1){--..}, at: [<c01299ae>] copy_process+0xac4/0x12bf > #2: (&mm->page_table_lock){--..}, at: [<c010334a>] xen_dup_mmap+0x11/0x24 > #3: (__pte_lockptr(new)){--..}, at: [<c0102d85>] lock_pte+0x10/0x15 > > stack backtrace: > [<c0109282>] show_trace_log_lvl+0x1a/0x2f > [<c0109d18>] show_trace+0x12/0x14 > [<c0109d30>] dump_stack+0x16/0x18 > [<c0147bd0>] __lock_acquire+0x195/0xc5f > [<c0148722>] lock_acquire+0x88/0xac > [<c035c2a3>] _spin_lock+0x35/0x42 > [<c0102d85>] lock_pte+0x10/0x15 > [<c010347d>] pin_page+0x67/0x17e > [<c0102d23>] pgd_walk+0x168/0x1ba > [<c0103283>] xen_pgd_pin+0x42/0xf8 > [<c0103352>] xen_dup_mmap+0x19/0x24 > [<c0129b63>] copy_process+0xc79/0x12bf > [<c012a419>] do_fork+0x99/0x1bf > [<c0106216>] sys_clone+0x33/0x39 > [<c010814e>] syscall_call+0x7/0xb > ======================= > > > I presume this is because I'm holding multiple pte locks (class > "__pte_lockptr(new)"). Is there some way I can tell lockdep this is OK? Yeah, the typical way is to use spin_lock_nested(lock, nesting_level), this allows one to annotate these nestings. However, nesting_level must not be larger than 8, so if your batch is larger than that, we have a problem. > I'm presume I'm the first person to try holding multiple pte locks at > once, so there's no existing locking order for these locks. Not quite, things like copy_pte_range() take 2. > I'm always > traversing and locking the pagetable in virtual address order (and this > seems like a sane-enough rule for anyone else who wants to hold multiple > pte locks). I'm quite sure copy_pte_range() could be used so that it violates that order. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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