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Message-Id: <20250627135807.dd97ddf4cb6910df3c56e654@kernel.org>
Date: Fri, 27 Jun 2025 13:58:07 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
x86@...nel.org, Song Liu <songliubraving@...com>, Yonghong Song
<yhs@...com>, John Fastabend <john.fastabend@...il.com>, Hao Luo
<haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, Alan Maguire
<alan.maguire@...cle.com>, David Laight <David.Laight@...lab.com>, Thomas
Weißschuh <thomas@...ch.de>, Ingo Molnar
<mingo@...nel.org>
Subject: Re: [PATCHv3 perf/core 07/22] uprobes: Add do_ref_ctr argument to
uprobe_write function
On Wed, 25 Jun 2025 17:11:09 +0200
Jiri Olsa <olsajiri@...il.com> wrote:
> On Wed, Jun 25, 2025 at 03:42:59PM +0900, Masami Hiramatsu wrote:
> > On Thu, 5 Jun 2025 15:23:34 +0200
> > Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > > Making update_ref_ctr call in uprobe_write conditional based
> > > on do_ref_ctr argument. This way we can use uprobe_write for
> > > instruction update without doing ref_ctr_offset update.
> > >
> >
> > Can we just decouple this update from uprobe_write()?
> > If we do this exclusively, I think we can do something like;
> >
> > lock()
> > update_ref_ctr(uprobe, mm, +1);
> > ...
> > ret = uprobe_write();
> > ...
> > if (ret < 0)
> > update_ref_ctr(uprobe, mm, -1);
> > unlock()
> >
> > Thank you,
>
> it was the intention in the v1 but as Oleg pointed out [1] it won't
> work, because the set_orig_refctr part of this change does not know
> if the refctr should be really updated or not
Ah, uprobe_unregister() can not check the given uprobe failed to
update the code for each mm....
>
> while inside uprobe_write it happens right after verify callback and
> we make sure to update refctr only if the instruction was updated
OK. But this is very complicated. Eventually I think uprobe should
have a list of mm(or refcnt) to manage whether it is updated the
refcounter.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thanks,
>
> thanks,
> jirka
>
>
> [1] https://lore.kernel.org/bpf/20250427141335.GA9350@redhat.com/
>
> >
> >
> > > Acked-by: Oleg Nesterov <oleg@...hat.com>
> > > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > > ---
> > > include/linux/uprobes.h | 2 +-
> > > kernel/events/uprobes.c | 8 ++++----
> > > 2 files changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> > > index 518b26756469..5080619560d4 100644
> > > --- a/include/linux/uprobes.h
> > > +++ b/include/linux/uprobes.h
> > > @@ -200,7 +200,7 @@ extern unsigned long uprobe_get_trap_addr(struct pt_regs *regs);
> > > extern int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma, unsigned long vaddr, uprobe_opcode_t,
> > > bool is_register);
> > > extern int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma, const unsigned long opcode_vaddr,
> > > - uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify, bool is_register);
> > > + uprobe_opcode_t *insn, int nbytes, uprobe_write_verify_t verify, bool is_register, bool do_update_ref_ctr);
> > > extern struct uprobe *uprobe_register(struct inode *inode, loff_t offset, loff_t ref_ctr_offset, struct uprobe_consumer *uc);
> > > extern int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool);
> > > extern void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc);
> > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > > index 1e5dc3b30707..6795b8d82b9c 100644
> > > --- a/kernel/events/uprobes.c
> > > +++ b/kernel/events/uprobes.c
> > > @@ -492,12 +492,12 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > > bool is_register)
> > > {
> > > return uprobe_write(auprobe, vma, opcode_vaddr, &opcode, UPROBE_SWBP_INSN_SIZE,
> > > - verify_opcode, is_register);
> > > + verify_opcode, is_register, true /* do_update_ref_ctr */);
> > > }
> > >
> > > int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > > const unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
> > > - uprobe_write_verify_t verify, bool is_register)
> > > + uprobe_write_verify_t verify, bool is_register, bool do_update_ref_ctr)
> > > {
> > > const unsigned long vaddr = insn_vaddr & PAGE_MASK;
> > > struct mm_struct *mm = vma->vm_mm;
> > > @@ -538,7 +538,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > > }
> > >
> > > /* We are going to replace instruction, update ref_ctr. */
> > > - if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
> > > + if (do_update_ref_ctr && !ref_ctr_updated && uprobe->ref_ctr_offset) {
> > > ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);
> > > if (ret) {
> > > folio_put(folio);
> > > @@ -590,7 +590,7 @@ int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
> > >
> > > out:
> > > /* Revert back reference counter if instruction update failed. */
> > > - if (ret < 0 && ref_ctr_updated)
> > > + if (do_update_ref_ctr && ret < 0 && ref_ctr_updated)
> > > update_ref_ctr(uprobe, mm, is_register ? -1 : 1);
> > >
> > > /* try collapse pmd for compound page */
> > > --
> > > 2.49.0
> > >
> >
> >
> > --
> > Masami Hiramatsu (Google) <mhiramat@...nel.org>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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