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.
WARNING: multiple messages have this Message-ID (diff)
From: oleg@redhat.com (Oleg Nesterov) To: linux-arm-kernel@lists.infradead.org Subject: [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: 84+ 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 ` Ravi Bangoria 2018-08-09 4:18 ` [PATCH v8 1/6] Uprobes: Simplify uprobe_register() body Ravi Bangoria 2018-08-09 4:18 ` Ravi Bangoria 2018-08-11 8:00 ` Song Liu 2018-08-11 8:00 ` Song Liu 2018-08-13 8:56 ` Srikar Dronamraju 2018-08-13 8:56 ` Srikar Dronamraju 2018-08-14 0:07 ` Steven Rostedt 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 2018-08-09 4:18 ` Ravi Bangoria 2018-08-11 8:01 ` Song Liu 2018-08-11 8:01 ` Song Liu 2018-08-13 8:51 ` Srikar Dronamraju 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 4:18 ` Ravi Bangoria 2018-08-09 14:38 ` Oleg Nesterov 2018-08-09 14:38 ` Oleg Nesterov 2018-08-10 19:58 ` Steven Rostedt 2018-08-10 19:58 ` Steven Rostedt 2018-08-11 6:14 ` Song Liu 2018-08-11 6:14 ` Song Liu 2018-08-14 0:01 ` Steven Rostedt 2018-08-14 0:01 ` Steven Rostedt 2018-08-14 0:05 ` Steven Rostedt 2018-08-14 0:05 ` Steven Rostedt 2018-08-11 7:57 ` Song Liu 2018-08-11 7:57 ` Song Liu 2018-08-11 15:37 ` Steven Rostedt 2018-08-11 15:37 ` Steven Rostedt 2018-08-13 5:47 ` Ravi Bangoria 2018-08-13 5:47 ` Ravi Bangoria 2018-08-13 7:38 ` Ravi Bangoria 2018-08-13 7:38 ` Ravi Bangoria 2018-08-13 11:50 ` Oleg Nesterov [this message] 2018-08-13 11:50 ` Oleg Nesterov 2018-08-13 13:01 ` Ravi Bangoria 2018-08-13 13:01 ` Ravi Bangoria 2018-08-13 13:17 ` Oleg Nesterov 2018-08-13 13:17 ` Oleg Nesterov 2018-08-13 14:26 ` Ravi Bangoria 2018-08-13 14:26 ` Ravi Bangoria 2018-08-13 14:51 ` Oleg Nesterov 2018-08-13 14:51 ` Oleg Nesterov 2018-08-13 17:12 ` Song Liu 2018-08-13 17:12 ` Song Liu 2018-08-14 4:37 ` Ravi Bangoria 2018-08-14 4:37 ` Ravi Bangoria 2018-08-14 16:35 ` Song Liu 2018-08-14 16:35 ` Song Liu 2018-08-14 0:03 ` Steven Rostedt 2018-08-14 0:03 ` Steven Rostedt 2018-08-13 16:50 ` Song Liu 2018-08-13 16:50 ` Song Liu 2018-08-13 10:03 ` Srikar Dronamraju 2018-08-13 10:03 ` Srikar Dronamraju 2018-08-13 11:23 ` Oleg Nesterov 2018-08-13 11:23 ` Oleg Nesterov 2018-08-14 8:56 ` Ravi Bangoria 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 2018-08-09 4:18 ` Ravi Bangoria 2018-08-11 8:04 ` Song Liu 2018-08-11 8:04 ` Song Liu 2018-08-13 8:50 ` Srikar Dronamraju 2018-08-13 8:50 ` Srikar Dronamraju 2018-08-09 4:18 ` [PATCH v8 5/6] trace_uprobe/sdt: " Ravi Bangoria 2018-08-09 4:18 ` Ravi Bangoria 2018-08-11 8:12 ` Song Liu 2018-08-11 8:12 ` Song Liu 2018-08-13 8:19 ` Ravi Bangoria 2018-08-13 8:19 ` Ravi Bangoria 2018-08-13 8:49 ` Srikar Dronamraju 2018-08-13 8:49 ` Srikar Dronamraju 2018-08-13 16:27 ` Song Liu 2018-08-13 16:27 ` Song Liu 2018-08-13 8:48 ` Srikar Dronamraju 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 2018-08-09 4:18 ` Ravi Bangoria 2018-08-13 16:55 ` [PATCH v8 0/6] Uprobes: Support SDT markers having reference count (semaphore) Oleg Nesterov 2018-08-13 16:55 ` Oleg Nesterov
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