From: Oleg Nesterov <oleg@redhat.com>
To: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: Song Liu <liu.song.a23@gmail.com>,
srikar@linux.vnet.ibm.com, Steven Rostedt <rostedt@goodmis.org>,
mhiramat@kernel.org, Peter Zijlstra <peterz@infradead.org>,
mingo@redhat.com, acme@kernel.org,
alexander.shishkin@linux.intel.com, jolsa@redhat.com,
namhyung@kernel.org, open list <linux-kernel@vger.kernel.org>,
ananth@linux.vnet.ibm.com,
Alexis Berlemont <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 13:50:19 +0200 [thread overview]
Message-ID: <20180813115019.GB28360@redhat.com> (raw)
In-Reply-To: <95a1221e-aecc-42be-5239-a2c2429be176@linux.ibm.com>
On 08/13, Ravi Bangoria wrote:
>
> On 08/11/2018 01:27 PM, Song Liu wrote:
> >> +
> >> +static void delayed_uprobe_delete(struct delayed_uprobe *du)
> >> +{
> >> + if (!du)
> >> + return;
> > Do we really need this check?
>
> Not necessary though, but I would still like to keep it for a safety.
Heh. I tried to ignore all minor problems in this version, but now that Song
mentioned this unnecessary check...
Personally I really dislike the checks like this one.
- It can confuse the reader who will try to understand the purpose
- it can hide a bug if delayed_uprobe_delete(du) is actually called
with du == NULL.
IMO, you should either remove it and let the kernel crash (to notice the
problem), or turn it into
if (WARN_ON(!du))
return;
which is self-documented and reports the problem without kernel crash.
> >> + rc_vma = find_ref_ctr_vma(uprobe, mm);
> >> +
> >> + if (rc_vma) {
> >> + rc_vaddr = offset_to_vaddr(rc_vma, uprobe->ref_ctr_offset);
> >> + ret = __update_ref_ctr(mm, rc_vaddr, is_register ? 1 : -1);
> >> +
> >> + if (is_register)
> >> + return ret;
> >> + }
> > Mixing __update_ref_ctr() here and delayed_uprobe_add() in the same
> > function is a little confusing (at least for me). How about we always use
> > delayed uprobe for uprobe_mmap() and use non-delayed in other case(s)?
>
>
> No. delayed_uprobe_add() is needed for uprobe_register() case to handle race
> between uprobe_register() and process creation.
Yes.
But damn, process creation (exec) is trivial. We could add a new uprobe_exec()
hook and avoid delayed_uprobe_install() in uprobe_mmap().
Afaics, the really problematic case is dlopen() which can race with _register()
too, right?
Oleg.
next prev parent reply other threads:[~2018-08-13 11:50 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 [this message]
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
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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