On Wed, 4 Nov 2020 09:47:22 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Wed, 4 Nov 2020 11:08:52 +0900 > Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > > kretprobe_hash_lock() and kretprobe_table_lock() will be called from > > outside of the kprobe pre_handler context. So, please keep in_nmi() > > in those functions. > > for the pre_handler_kretprobe(), this looks good to me. > > > > Final version, before sending to Linus. This looks good to me :) Thank you! > > -- Steve > > From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> > Subject: [PATCH] kprobes: Tell lockdep about kprobe nesting > > Since the kprobe handlers have protection that prohibits other handlers from > executing in other contexts (like if an NMI comes in while processing a > kprobe, and executes the same kprobe, it will get fail with a "busy" > return). Lockdep is unaware of this protection. Use lockdep's nesting api to > differentiate between locks taken in INT3 context and other context to > suppress the false warnings. > > Link: https://lore.kernel.org/r/20201102160234.fa0ae70915ad9e2b21c08b85@xxxxxxxxxx > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > --- > kernel/kprobes.c | 25 +++++++++++++++++++++---- > 1 file changed, 21 insertions(+), 4 deletions(-) > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 8a12a25fa40d..41fdbb7953c6 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -1249,7 +1249,13 @@ __acquires(hlist_lock) > > *head = &kretprobe_inst_table[hash]; > hlist_lock = kretprobe_table_lock_ptr(hash); > - raw_spin_lock_irqsave(hlist_lock, *flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + * Differentiate when it is taken in NMI context. > + */ > + raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi()); > } > NOKPROBE_SYMBOL(kretprobe_hash_lock); > > @@ -1258,7 +1264,13 @@ static void kretprobe_table_lock(unsigned long hash, > __acquires(hlist_lock) > { > raw_spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash); > - raw_spin_lock_irqsave(hlist_lock, *flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + * Differentiate when it is taken in NMI context. > + */ > + raw_spin_lock_irqsave_nested(hlist_lock, *flags, !!in_nmi()); > } > NOKPROBE_SYMBOL(kretprobe_table_lock); > > @@ -2028,7 +2040,12 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs) > > /* TODO: consider to only swap the RA after the last pre_handler fired */ > hash = hash_ptr(current, KPROBE_HASH_BITS); > - raw_spin_lock_irqsave(&rp->lock, flags); > + /* > + * Nested is a workaround that will soon not be needed. > + * There's other protections that make sure the same lock > + * is not taken on the same CPU that lockdep is unaware of. > + */ > + raw_spin_lock_irqsave_nested(&rp->lock, flags, 1); > if (!hlist_empty(&rp->free_instances)) { > ri = hlist_entry(rp->free_instances.first, > struct kretprobe_instance, hlist); > @@ -2039,7 +2056,7 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs) > ri->task = current; > > if (rp->entry_handler && rp->entry_handler(ri, regs)) { > - raw_spin_lock_irqsave(&rp->lock, flags); > + raw_spin_lock_irqsave_nested(&rp->lock, flags, 1); > hlist_add_head(&ri->hlist, &rp->free_instances); > raw_spin_unlock_irqrestore(&rp->lock, flags); > return 0; > -- > 2.25.4 > -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
