From: dimm <dmitry.adamushko@gmail.com>
To: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Subject: [PATCH] mips: fix endless loop when processing signals for kernel tasks
Date: Thu, 05 Apr 2012 20:37:34 +0200 [thread overview]
Message-ID: <1333651054.3680.11.camel@dimm> (raw)
From: Dmitry Adamushko <dmitry.adamushka_ext@softathome.com>
The problem occurs [1] when a kernel-mode task returns from a system
call with a pending signal.
A real-life scenario is a child of 'khelper' returning from a failed
kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ].
kernel_execve() fails due to a pending SIGKILL, which is the result of
"kill -9 -1" (at least, busybox's init does it upon reboot).
The loop is as follows:
* syscall_exit_work:
- work_pending: // start_of_the_loop
- work_notifysig:
- do_notify_resume()
- do_signal()
- if (!user_mode(regs)) return;
- resume_userspace // TIF_SIGPENDING is still set
- work_pending // so we call work_pending => goto
// start_of_the_loop
More information can be found in another LKML thread:
http://www.serverphorums.com/read.php?12,457826
[1] The problem was also reproduced on !CONFIG_VM86 x86, and the
following fix was accepted.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29a2e2836ff9ea65a603c89df217f4198973a74f
Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
--- arch/mips/kernel/entry.S.old 2012-04-05 10:57:12.500976124 +0200
+++ arch/mips/kernel/entry.S 2012-04-05 11:21:24.128174358 +0200
@@ -36,6 +36,11 @@ FEXPORT(ret_from_exception)
FEXPORT(ret_from_irq)
LONG_S s0, TI_REGS($28)
FEXPORT(__ret_from_irq)
+/*
+ * We can be coming here from a syscall done in the kernel space,
+ * e.g. a failed kernel_execve().
+ */
+resume_userspace_check:
LONG_L t0, PT_STATUS(sp) # returning to kernel mode?
andi t0, t0, KU_USER
beqz t0, resume_kernel
@@ -162,7 +167,7 @@ work_notifysig: # deal with pending s
move a0, sp
li a1, 0
jal do_notify_resume # a2 already loaded
- j resume_userspace
+ j resume_userspace_check
FEXPORT(syscall_exit_work_partial)
SAVE_STATIC
next reply other threads:[~2012-04-05 18:38 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-05 18:37 dimm [this message]
2012-05-17 6:37 ` [PATCH] mips: fix endless loop when processing signals for kernel tasks Dmitry Adamushko
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=1333651054.3680.11.camel@dimm \
--to=dmitry.adamushko@gmail.com \
--cc=linux-mips@linux-mips.org \
--cc=ralf@linux-mips.org \
/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