From: Frederic Weisbecker <fweisbec@gmail.com>
To: "K.Prasad" <prasad@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>,
Alan Stern <stern@rowland.harvard.edu>
Subject: Re: [RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code to notifier chain in hw_breakpoint_handler
Date: Mon, 25 Jan 2010 23:11:04 +0100 [thread overview]
Message-ID: <20100125221101.GE5087@nowhere> (raw)
In-Reply-To: <20091226182833.GC9494@in.ibm.com>
On Sat, Dec 26, 2009 at 11:58:33PM +0530, K.Prasad wrote:
> The hw-breakpoint handler will return NOTIFY_DONE for user-space breakpoints
> to generate SIGTRAP signal (and not for kernel-space addresses).
Please tell a bit more in your changelogs. It took me some time
to guess whether this is a fix or not.
And this is not a fix but an optimization because SIGTRAP
is only sent if needed.
Here is what happens in do_debug() after handling the
breakpoint:
if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS))
send_sigtrap(tsk, regs, error_code, si_code);
This can only happen if we took the ptrace handler path.
Also:
> Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
> ---
> arch/x86/kernel/hw_breakpoint.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> Index: linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c
> ===================================================================
> --- linux-2.6-tip.orig/arch/x86/kernel/hw_breakpoint.c
> +++ linux-2.6-tip/arch/x86/kernel/hw_breakpoint.c
> @@ -502,8 +502,6 @@ static int __kprobes hw_breakpoint_handl
> rcu_read_lock();
>
> bp = per_cpu(bp_per_reg[i], cpu);
> - if (bp)
> - rc = NOTIFY_DONE;
> /*
> * Reset the 'i'th TRAP bit in dr6 to denote completion of
> * exception handling
> @@ -517,6 +515,13 @@ static int __kprobes hw_breakpoint_handl
> rcu_read_unlock();
> break;
> }
> + /*
> + * Further processing in do_debug() is needed for a) user-space
> + * breakpoints (to generate signals) and b) when the system has
> + * taken exception due to multiple causes
> + */
> + if (bp->attr.bp_addr < TASK_SIZE)
> + rc = NOTIFY_DONE;
Is that < TASK_SIZE an accurate check? We want support for
userspace breakpoints on perf tools later, and those don't want
signals.
We do this cleanup in the beginning of the breakpoint handler:
current->thread.debugreg6 &= ~DR_TRAP_BITS;
And from ptrace.c:ptrace_triggered():
thread->debugreg6 |= (DR_TRAP0 << i);
This is called on perf_bp_event().
Instead of checking if this is a userspace thread, we should actually
check if this is a ptrace breakpoint by looking at this
in the end of hw_breakpoint_handler().
current->thread.debugreg6 & DR_TRAP_BITS
Only ptrace breakpoints require signals.
Thanks.
next prev parent reply other threads:[~2010-01-25 22:11 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20091226175533.149765731@linux.vnet.ibm.com>
2009-12-26 18:27 ` [RFC Patch 1/2][Bugfix][x86][hw-breakpoint] Clear reserved bits of DR6 in do_debug() K.Prasad
2009-12-30 23:45 ` Frederic Weisbecker
2009-12-31 18:49 ` K.Prasad
2010-01-10 3:22 ` Frederic Weisbecker
2009-12-26 18:28 ` [RFC Patch 2/2][Bugfix][x86][hw-breakpoint] Fix return-code to notifier chain in hw_breakpoint_handler K.Prasad
2009-12-31 0:33 ` Frederic Weisbecker
2009-12-31 0:38 ` Frederic Weisbecker
2009-12-31 19:02 ` K.Prasad
2010-01-10 3:18 ` Frederic Weisbecker
2010-01-11 19:15 ` Jan Kiszka
2010-01-16 19:41 ` K.Prasad
2010-01-20 6:01 ` K.Prasad
2010-01-22 9:14 ` Jan Kiszka
2010-01-22 9:21 ` K.Prasad
2010-01-25 22:21 ` Frederic Weisbecker
2010-01-27 10:29 ` K.Prasad
2009-12-31 0:44 ` Frederic Weisbecker
2010-01-25 22:11 ` Frederic Weisbecker [this message]
2010-01-27 10:28 ` K.Prasad
2010-01-27 16:11 ` Frederic Weisbecker
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100125221101.GE5087@nowhere \
--to=fweisbec@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=prasad@linux.vnet.ibm.com \
--cc=stern@rowland.harvard.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).