From: Oleg Nesterov <oleg@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>,
rostedt@goodmis.org, mhiramat@kernel.org, liu.song.a23@gmail.com,
peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
alexander.shishkin@linux.intel.com, jolsa@redhat.com,
namhyung@kernel.org, linux-kernel@vger.kernel.org,
ananth@linux.vnet.ibm.com, alexis.berlemont@gmail.com,
naveen.n.rao@linux.vnet.ibm.com,
linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org,
linux@armlinux.org.uk, ralf@linux-mips.org, paul.burton@mips.com
Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)
Date: Mon, 13 Aug 2018 13:23:25 +0200 [thread overview]
Message-ID: <20180813112324.GA28360@redhat.com> (raw)
In-Reply-To: <20180813100327.GF44470@linux.vnet.ibm.com>
On 08/13, Srikar Dronamraju wrote:
>
> > +
> > +static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
> > +{
> > + struct delayed_uprobe *du;
> > +
> > + if (delayed_uprobe_check(uprobe, mm))
> > + return 0;
> > +
> > + du = kzalloc(sizeof(*du), GFP_KERNEL);
> > + if (!du)
> > + return -ENOMEM;
> > +
> > + du->uprobe = uprobe;
> > + du->mm = mm;
> > + list_add(&du->list, &delayed_uprobe_list);
> > + return 0;
> > +}
> > +
>
> Should we keep the delayed uprobe list per mm?
> That way we could avoid the global mutex lock.
> And the list to traverse would also be small.
Plus uprobe_mmap() could simply check list_empty(mm->delayed_list) before
the costly delayed_uprobe_install().
Yes, I mentioned this too. But then I suggested to not do this in the initial
version to make it more simple.
Hopefully we can do this later, but note that this conflicts with the change
in put_uprobe() you commented below.
> > static void put_uprobe(struct uprobe *uprobe)
> > {
> > - if (atomic_dec_and_test(&uprobe->ref))
> > + if (atomic_dec_and_test(&uprobe->ref)) {
> > + /*
> > + * If application munmap(exec_vma) before uprobe_unregister()
> > + * gets called, we don't get a chance to remove uprobe from
> > + * delayed_uprobe_list in remove_breakpoint(). Do it here.
> > + */
> > + delayed_uprobe_remove(uprobe, NULL);
>
> I am not getting this part. If unmap happens before unregister,
> why cant we use uprobe_munmap?
How? I mean what exactly can we do in uprobe_munmap() ? Firstly, we will need
to restore build_probe_list/list_for_each_entry_safe(pending_list) in
uprobe_munmap() and this is not nice performance-wise. Then what?
We don't even know if the caller is actually munmap(), it can be vma_adjust()
and in the latter case we can't do delayed_uprobe_remove(uprobe, mm).
Perhaps we can use uprobe_munmap() to cleanup the delayed_uprobe_list, but this
doesn't look simple to me.
In fact I think that we should simply kill uprobe_munmap().
Oleg.
next prev parent reply other threads:[~2018-08-13 11:23 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-09 4:18 [PATCH v8 0/6] Uprobes: Support SDT markers having reference count (semaphore) Ravi Bangoria
2018-08-09 4:18 ` [PATCH v8 1/6] Uprobes: Simplify uprobe_register() body Ravi Bangoria
2018-08-11 8:00 ` Song Liu
2018-08-13 8:56 ` Srikar Dronamraju
2018-08-14 0:07 ` Steven Rostedt
2018-08-09 4:18 ` [PATCH v8 2/6] Uprobe: Additional argument arch_uprobe to uprobe_write_opcode() Ravi Bangoria
2018-08-11 8:01 ` Song Liu
2018-08-13 8:51 ` Srikar Dronamraju
2018-08-09 4:18 ` [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) Ravi Bangoria
2018-08-09 14:38 ` Oleg Nesterov
2018-08-10 19:58 ` Steven Rostedt
2018-08-11 6:14 ` Song Liu
2018-08-14 0:01 ` Steven Rostedt
2018-08-14 0:05 ` Steven Rostedt
2018-08-11 7:57 ` Song Liu
2018-08-11 15:37 ` Steven Rostedt
2018-08-13 5:47 ` Ravi Bangoria
2018-08-13 7:38 ` Ravi Bangoria
2018-08-13 11:50 ` Oleg Nesterov
2018-08-13 13:01 ` Ravi Bangoria
2018-08-13 13:17 ` Oleg Nesterov
2018-08-13 14:26 ` Ravi Bangoria
2018-08-13 14:51 ` Oleg Nesterov
2018-08-13 17:12 ` Song Liu
2018-08-14 4:37 ` Ravi Bangoria
2018-08-14 16:35 ` Song Liu
2018-08-14 0:03 ` Steven Rostedt
2018-08-13 16:50 ` Song Liu
2018-08-13 10:03 ` Srikar Dronamraju
2018-08-13 11:23 ` Oleg Nesterov [this message]
2018-08-14 8:56 ` Ravi Bangoria
2018-08-09 4:18 ` [PATCH v8 4/6] Uprobes/sdt: Prevent multiple reference counter for same uprobe Ravi Bangoria
2018-08-11 8:04 ` Song Liu
2018-08-13 8:50 ` Srikar Dronamraju
2018-08-09 4:18 ` [PATCH v8 5/6] trace_uprobe/sdt: " Ravi Bangoria
2018-08-11 8:12 ` Song Liu
2018-08-13 8:19 ` Ravi Bangoria
2018-08-13 8:49 ` Srikar Dronamraju
2018-08-13 16:27 ` Song Liu
2018-08-13 8:48 ` Srikar Dronamraju
2018-08-09 4:18 ` [PATCH v8 6/6] perf probe: Support SDT markers having reference counter (semaphore) Ravi Bangoria
2018-08-13 16:55 ` [PATCH v8 0/6] Uprobes: Support SDT markers having reference count (semaphore) Oleg Nesterov
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