Messages in this thread | | | Date | Thu, 10 Jun 2010 16:38:15 -0400 | From | tytso@mit ... | Subject | Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately. |
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On Thu, Jun 10, 2010 at 01:09:11PM -0700, Salman wrote: > A program that repeatedly forks and waits is susceptible to having the > same pid repeated, especially when it competes with another instance of the > same program. This is really bad for bash implementation. Furthermore, many shell > scripts assume that pid numbers will not be used for some length of time.
This should probably get wrapped at column 74 or so....
> +static int pid_before(int base, int a, int b) > +{ > + /* > + * This is the same as saying > + * > + * (a - base + MAXUINT) % MAXUINT < (b - base + MAXUINT) % MAXUINT > + * and that mapping orders 'a' and 'b' with respect to 'base'. > + * > + */ > + return (unsigned)(a - base) < (unsigned)(b - base); > +}
Does this work though if /proc/sys/kernel/pid_max is not set to MAXUINT?
I like the optimization, but it looks like pid_max defaults to 4096 if CONFIG_BASE_SMALL is set, and 32768 otherwise.
Am I missing something?
- Ted
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