From b470030f839a375e5030ec9d44903ef7581c15a2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Thu, 24 Mar 2011 14:18:00 -0400 Subject: 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... --- arch/i386/pthread_arch.h | 3 +++ arch/x86_64/pthread_arch.h | 3 +++ 2 files changed, 6 insertions(+) (limited to 'arch') 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) -- cgit v1.2.3-70-g09d2