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fix race condition in raise - just mask signals 

a signal handler could fork after the pid/tid were read, causing the
wrong process to be signalled. i'm not sure if this is supposed to
have UB or not, but raise is async-signal-safe, so it probably is
allowed. the current solution is slightly expensive so this
implementation is likely to be changed in the future.
This commit is contained in:
Rich Felker 2011-03-09 20:07:24 -05:00
parent 370f78f2c8
commit 0bed7e0acf
1 changed files with 9 additions and 9 deletions
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18
src/signal/raise.c
View File

@ -2,17 +2,17 @@
#include <errno.h>
#include "syscall.h"
int __sigprocmask(int, const sigset_t *, sigset_t *);
int raise(int sig)
{
int pid, tid, ret;
/* Getting the pid/tid pair is not atomic, and could give wrong
* result if a fork occurs in a signal handler between the two
* syscalls. Use the tgkill syscall's ESRCH semantics to detect
* this condition and retry. */
do {
tid = syscall0(__NR_gettid);
pid = syscall0(__NR_getpid);
ret = syscall3(__NR_tgkill, pid, tid, sig);
} while (ret<0 && errno == ESRCH);
sigset_t set;
sigfillset(&set);
__sigprocmask(SIG_BLOCK, &set, &set);
tid = syscall0(__NR_gettid);
pid = syscall0(__NR_getpid);
ret = syscall3(__NR_tgkill, pid, tid, sig);
__sigprocmask(SIG_SETMASK, &set, 0);
return ret;
}