path: root/arch
diff options
authorRich Felker <>2011-03-24 14:18:00 -0400
committerRich Felker <>2011-03-24 14:18:00 -0400
commitb470030f839a375e5030ec9d44903ef7581c15a2 (patch)
tree462b1df89a3ea45bcf50b9d0a844472576ed6585 /arch
parent095820016689dfdc9141f477a86de22054c86078 (diff)
overhaul cancellation to fix resource leaks and dangerous behavior with signals
this commit addresses two issues: 1. a race condition, whereby a cancellation request occurring after a syscall returned from kernelspace but before the subsequent CANCELPT_END would cause cancellable resource-allocating syscalls (like open) to leak resources. 2. signal handlers invoked while the thread was blocked at a cancellation point behaved as if asynchronous cancellation mode wer in effect, resulting in potentially dangerous state corruption if a cancellation request occurs. the glibc/nptl implementation of threads shares both of these issues. with this commit, both are fixed. however, cancellation points encountered in a signal handler will not be acted upon if the signal was received while the thread was already at a cancellation point. they will of course be acted upon after the signal handler returns, so in real-world usage where signal handlers quickly return, it should not be a problem. it's possible to solve this problem too by having sigaction() wrap all signal handlers with a function that uses a pthread_cleanup handler to catch cancellation, patch up the saved context, and return into the cancellable function that will catch and act upon the cancellation. however that would be a lot of complexity for minimal if any benefit...
Diffstat (limited to 'arch')
2 files changed, 6 insertions, 0 deletions
diff --git a/arch/i386/pthread_arch.h b/arch/i386/pthread_arch.h
index 155b4847..64d75cbc 100644
--- a/arch/i386/pthread_arch.h
+++ b/arch/i386/pthread_arch.h
@@ -4,3 +4,6 @@ static inline struct pthread *__pthread_self()
__asm__ ("movl %%gs:0,%0" : "=r" (self) );
return self;
+#define PC_AT_SYS(c) \
+ (*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[14])==0x80cd)
diff --git a/arch/x86_64/pthread_arch.h b/arch/x86_64/pthread_arch.h
index 40d26797..af7ae86e 100644
--- a/arch/x86_64/pthread_arch.h
+++ b/arch/x86_64/pthread_arch.h
@@ -4,3 +4,6 @@ static inline struct pthread *__pthread_self()
__asm__ ("movq %%fs:0,%0" : "=r" (self) );
return self;
+#define PC_AT_SYS(c) \
+ (*(uint16_t *)(((ucontext_t *)(c))->uc_mcontext.__gregs[16])==0x050f)