diff options
authorJohn Blackwood <john.blackwood@ccur.com>2006-02-12 14:34:58 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-02-12 16:10:47 -0800
commita65d17c9d27a85782cfe1bbc36c747ffa1f81814 (patch)
parent8f6da52aeff1fd7272ff5082552a39c050565b57 (diff)
[PATCH] arch/x86_64/kernel/traps.c PTRACE_SINGLESTEP oops
We found a problem with x86_64 kernels with preemption enabled, where having multiple tasks doing ptrace singlesteps around the same time will cause the system to 'oops'. The problem seems that a task can get preempted out of the do_debug() processing while it is running on the DEBUG_STACK stack. If another task on that same cpu then enters do_debug() and uses the same per-cpu DEBUG_STACK stack, the previous preempted tasks's stack contents can be corrupted, and the system will oops when the preempted task is context switched back in again. The typical oops looks like the following: Unable to handle kernel paging request at ffffffffffffffae RIP: <ffffffff805452a1>{thread_return+34} PGD 103027 PUD 102429067 PMD 0 Oops: 0002 [1] PREEMPT SMP CPU 0 Modules linked in: Pid: 3786, comm: ssdd Not tainted #1 RIP: 0010:[<ffffffff805452a1>] <ffffffff805452a1>{thread_return+34} RSP: 0018:ffffffff80824058 EFLAGS: 000136c2 RAX: ffff81017e12cea0 RBX: 0000000000000000 RCX: 00000000c0000100 RDX: 0000000000000000 RSI: ffff8100f7856e20 RDI: ffff81017e12cea0 RBP: 0000000000000046 R08: ffff8100f68a6000 R09: 0000000000000000 R10: 0000000000000000 R11: ffff81017e12cea0 R12: ffff81000c2d53e8 R13: ffff81017f5b3be8 R14: ffff81000c0036e0 R15: 000001056cbfc899 FS: 00002aaaaaad9b00(0000) GS:ffffffff80883800(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b CR2: ffffffffffffffae CR3: 00000000f6fcf000 CR4: 00000000000006e0 Process ssdd (pid: 3786, threadinfo ffff8100f68a6000, task ffff8100f7856e20) Stack: ffffffff808240d8 ffffffff8012a84a ffff8100055f6c00 0000000000000020 0000000000000001 ffff81000c0036e0 ffffffff808240b8 0000000000000000 0000000000000000 0000000000000000 Call Trace: <#DB> <ffffffff8012a84a>{try_to_wake_up+985} <ffffffff8012c0d3>{kick_process+87} <ffffffff8013b262>{signal_wake_up+48} <ffffffff8013b5ce>{specific_send_sig_info+179} <ffffffff80546abc>{_spin_unlock_irqrestore+27} <ffffffff8013b67c>{force_sig_info+159} <ffffffff801103a0>{do_debug+289} <ffffffff80110278>{sync_regs+103} <ffffffff8010ed9a>{paranoid_userspace+35} Unable to handle kernel paging request at 00007fffffb7d000 RIP: <ffffffff8010f2e4>{show_trace+465} PGD f6f25067 PUD f6fcc067 PMD f6957067 PTE 0 Oops: 0000 [2] PREEMPT SMP This patch disables preemptions for the task upon entry to do_debug(), before interrupts are reenabled, and then disables preemption before exiting do_debug(), after disabling interrupts. I've noticed that the task can be preempted either at the end of an interrupt, or on the call to force_sig_info() on the spin_unlock_irqrestore() processing. It might be better to attempt to code a fix in entry.S around the code that calls do_debug(). Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 files changed, 17 insertions, 1 deletions
diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index ee1b2da9e5e..28d50dc540e 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -90,6 +90,20 @@ static inline void conditional_sti(struct pt_regs *regs)
+static inline void preempt_conditional_sti(struct pt_regs *regs)
+ preempt_disable();
+ if (regs->eflags & X86_EFLAGS_IF)
+ local_irq_enable();
+static inline void preempt_conditional_cli(struct pt_regs *regs)
+ if (regs->eflags & X86_EFLAGS_IF)
+ local_irq_disable();
+ preempt_enable_no_resched();
static int kstack_depth_to_print = 10;
@@ -693,7 +707,7 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs,
- conditional_sti(regs);
+ preempt_conditional_sti(regs);
/* Mask out spurious debug traps due to lazy DR7 setting */
if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
@@ -738,11 +752,13 @@ asmlinkage void __kprobes do_debug(struct pt_regs * regs,
set_debugreg(0UL, 7);
+ preempt_conditional_cli(regs);
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
regs->eflags &= ~TF_MASK;
+ preempt_conditional_cli(regs);
static int kernel_math_error(struct pt_regs *regs, const char *str, int trapnr)