diff options
Diffstat (limited to 'man2/tkill.2')
| -rw-r--r-- | man2/tkill.2 | 38 |
1 files changed, 20 insertions, 18 deletions
diff --git a/man2/tkill.2 b/man2/tkill.2 index be0e2e416d..a61ef31821 100644 --- a/man2/tkill.2 +++ b/man2/tkill.2 @@ -61,27 +61,29 @@ terminates and its thread ID is recycled. Avoid using this system call. .\" FIXME Maybe say something about the following: .\" http://sourceware.org/bugzilla/show_bug.cgi?id=12889 -.\" Rich Felker <bugdal@aerifal.cx> -.\" There is a race condition in pthread_kill: it is possible that, -.\" between the time pthread_kill reads the pid/tid from the target -.\" thread descriptor and the time it makes the tgkill syscall, -.\" the target thread terminates and the same tid gets assigned -.\" to a new thread in the same process. .\" -.\" (The tgkill syscall was designed to eliminate a similar race -.\" condition in tkill, but it only succeeded in eliminating races -.\" where the tid gets reused in a different process, and does not -.\" help if the same tid gets assigned to a new thread in the -.\" same process.) +.\" Quoting Rich Felker <bugdal@aerifal.cx>: .\" -.\" The only solution I can see is to introduce a mutex that ensures -.\" that a thread cannot exit while pthread_kill is being called on it. +.\" There is a race condition in pthread_kill: it is possible that, +.\" between the time pthread_kill reads the pid/tid from the target +.\" thread descriptor and the time it makes the tgkill syscall, +.\" the target thread terminates and the same tid gets assigned +.\" to a new thread in the same process. .\" -.\" Note that in most real-world situations, like almost all race -.\" conditions, this one will be extremely rare. To make it -.\" measurable, one could exhaust all but 1-2 available pid values, -.\" possibly by lowering the max pid parameter in /proc, forcing -.\" the same tid to be reused rapidly. +.\" (The tgkill syscall was designed to eliminate a similar race +.\" condition in tkill, but it only succeeded in eliminating races +.\" where the tid gets reused in a different process, and does not +.\" help if the same tid gets assigned to a new thread in the +.\" same process.) +.\" +.\" The only solution I can see is to introduce a mutex that ensures +.\" that a thread cannot exit while pthread_kill is being called on it. +.\" +.\" Note that in most real-world situations, like almost all race +.\" conditions, this one will be extremely rare. To make it +.\" measurable, one could exhaust all but 1-2 available pid values, +.\" possibly by lowering the max pid parameter in /proc, forcing +.\" the same tid to be reused rapidly. These are the raw system call interfaces, meant for internal thread library use. |