From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Cc: oleg@redhat.com, peterz@infradead.org, srikar@linux.vnet.ibm.com,
rostedt@goodmis.org, acme@kernel.org, ananth@linux.vnet.ibm.com,
akpm@linux-foundation.org, alexander.shishkin@linux.intel.com,
alexis.berlemont@gmail.com, corbet@lwn.net,
dan.j.williams@intel.com, jolsa@redhat.com, kan.liang@intel.com,
kjlx@templeofstupid.com, kstewart@linuxfoundation.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, milian.wolff@kdab.com, mingo@redhat.com,
namhyung@kernel.org, naveen.n.rao@linux.vnet.ibm.com,
pc@us.ibm.com, tglx@linutronix.de, yao.jin@linux.intel.com,
fengguang.wu@intel.com, jglisse@redhat.com
Subject: Re: [PATCH v3 6/9] trace_uprobe: Support SDT markers having reference count (semaphore)
Date: Tue, 8 May 2018 00:56:51 +0900 [thread overview]
Message-ID: <20180508005651.45553d3cf72521481d16b801@kernel.org> (raw)
In-Reply-To: <f3d066d2-a85a-bd21-d4f9-fc27e59135df@linux.ibm.com>
On Mon, 7 May 2018 13:51:21 +0530
Ravi Bangoria <ravi.bangoria@linux.ibm.com> wrote:
> Hi Masami,
>
> On 05/04/2018 07:51 PM, Ravi Bangoria wrote:
> >
> >>> +}
> >>> +
> >>> +static void sdt_increment_ref_ctr(struct trace_uprobe *tu)
> >>> +{
> >>> + struct uprobe_map_info *info;
> >>> +
> >>> + uprobe_down_write_dup_mmap();
> >>> + info = uprobe_build_map_info(tu->inode->i_mapping,
> >>> + tu->ref_ctr_offset, false);
> >>> + if (IS_ERR(info))
> >>> + goto out;
> >>> +
> >>> + while (info) {
> >>> + down_write(&info->mm->mmap_sem);
> >>> +
> >>> + if (sdt_find_vma(tu, info->mm, info->vaddr))
> >>> + sdt_update_ref_ctr(info->mm, info->vaddr, 1);
> >> Don't you have to handle the error to map pages here?
> > Correct.. I think, I've to feedback error code to probe_event_{enable|disable}
> > and handler failure there.
>
> I looked at this. Actually, It looks difficult to feedback errors to
> probe_event_{enable|disable}, esp. in the mmap() case.
Hmm, can't you roll that back if sdt_increment_ref_ctr() fails?
If so, how does sdt_decrement_ref_ctr() work in that case?
> Is it fine if we just warn sdt_update_ref_ctr() failures in dmesg? I'm
> doing this in [PATCH 7]. (Though, it makes more sense to do that in
> [PATCH 6], will change it in next version).
Of course we need to warn it at least, but the best is rejecting to
enable it.
>
> Any better ideas?
>
> BTW, same issue exists for normal uprobe. If uprobe_mmap() fails,
> there is no feedback to trace_uprobe and no warnigns in dmesg as
> well !! There was a patch by Naveen to warn such failures in dmesg
> but that didn't go in: https://lkml.org/lkml/2017/9/22/155
Oops, that's a real bug. It seems the ball is in Naveen's hand.
Naveen, could you update it according to Oleg's comment, and resend it?
>
> Also, I'll add a check in sdt_update_ref_ctr() to make sure reference
> counter never goes to negative incase increment fails but decrement
> succeeds. OTOH, if increment succeeds but decrement fails, the
> counter remains >0 but there is no harm as such, except we will
> execute some unnecessary code.
I see. Please carefully clarify whether such case is kernel's bug or not.
I would like to know what the condition causes that uneven behavior.
Thank you,
>
> Thanks,
> Ravi
>
--
Masami Hiramatsu <mhiramat@kernel.org>
next prev parent reply other threads:[~2018-05-07 15:56 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-17 4:32 [PATCH v3 0/9] trace_uprobe: Support SDT markers having reference count (semaphore) Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 1/9] Uprobe: Export vaddr <-> offset conversion functions Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 2/9] mm: Prefix vma_ to vaddr_to_offset() and offset_to_vaddr() Ravi Bangoria
2018-05-03 14:59 ` Steven Rostedt
2018-04-17 4:32 ` [PATCH v3 3/9] Uprobe: Move mmput() into free_map_info() Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 4/9] Uprobe: Rename map_info to uprobe_map_info Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 5/9] Uprobe: Export uprobe_map_info along with uprobe_{build/free}_map_info() Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 6/9] trace_uprobe: Support SDT markers having reference count (semaphore) Ravi Bangoria
2018-05-04 4:48 ` Masami Hiramatsu
2018-05-04 14:21 ` Ravi Bangoria
2018-05-07 8:21 ` Ravi Bangoria
2018-05-07 15:56 ` Masami Hiramatsu [this message]
2018-05-08 9:46 ` Naveen N. Rao
2018-05-08 10:26 ` Ravi Bangoria
2018-05-24 16:26 ` Oleg Nesterov
2018-05-25 8:28 ` Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 7/9] trace_uprobe/sdt: Fix multiple update of same reference counter Ravi Bangoria
2018-04-17 4:32 ` [PATCH v3 8/9] trace_uprobe/sdt: Document about " Ravi Bangoria
2018-05-03 14:57 ` Masami Hiramatsu
2018-04-17 4:32 ` [PATCH v3 9/9] perf probe: Support SDT markers having reference counter (semaphore) Ravi Bangoria
2018-05-03 14:57 ` Masami Hiramatsu
2018-05-03 8:32 ` [PATCH v3 0/9] trace_uprobe: Support SDT markers having reference count (semaphore) Ravi Bangoria
2018-05-04 14:30 ` Oleg Nesterov
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