linux-mips
[Top] [All Lists]

[PATCH] mips: fix endless loop when processing signals for kernel tasks

To: Ralf Baechle <ralf@linux-mips.org>
Subject: [PATCH] mips: fix endless loop when processing signals for kernel tasks
From: dimm <dmitry.adamushko@gmail.com>
Date: Thu, 05 Apr 2012 20:37:34 +0200
Cc: linux-mips@linux-mips.org
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:from:to:cc:content-type:date:message-id:mime-version :x-mailer:content-transfer-encoding; bh=UYRGSNYuaPrcuTTxZZpdBdLtYo1uIiSqKXvur1rj4g0=; b=fclZzgLCkqYxa0edQ56xLrsD73y1bacG4amLyjEwP0CEVgz3Qj2Vx1Rqz7uKZER9Tt 8U6cADx4oomtVrsRW6y+04f+x0XXFrqd1nYhOxWknof5MCeB7w5bQypQsg3e01AHPaQ4 sZDXXj4TKWYey8obnXYFAkGkpIyIi34B9MLsq0eJ/JRXnG3e8x7k2HeREQvg+E7GSF5L B3FWEUrU7BMt87BTQHEN9ueAuSF1GtS9rOluKoiKCD/r2oBhOUbM4iDZIjN8PtGQenl6 rNxRW4xjloYC5MIDDPR7Hd09BJm5OjUiUpsmcaivPOOVJbYfQt3ELu36R/vl2IcFPAQ/ pgHw==
Sender: linux-mips-bounce@linux-mips.org
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



<Prev in Thread] Current Thread [Next in Thread>
  • [PATCH] mips: fix endless loop when processing signals for kernel tasks, dimm <=