On Thu, Apr 11, 2013 at 11:43:31AM -0500, Serge Hallyn wrote: > 1. in container_free, set c->privlock to NULL before calling > sem_destroy, to prevent a window where another thread could call > sem_wait(c->privlock) while c->privlock is not NULL but is already > destroyed. > > 2. in container_get, check for numthreads < 0 before calling lxclock. > Once numthreads is 0, it never goes back up. > > Following is a comment added to lxccontainer.c: > > /* > * Consider the following case: > freer | racing get()er > ================================================================== > lxc_container_put() | lxc_container_get() > \ lxclock(c->privlock) | c->numthreads < 1? (no) > \ c->numthreads = 0 | \ lxclock(c->privlock) -> waits > \ lxcunlock() | \ > \ lxc_container_free() | \ lxclock() returns > | \ c->numthreads < 1 -> return 0 > \ \ (free stuff) | > \ \ sem_destroy(privlock) | > > * When the get()er checks numthreads the first time, one of the following > * is true: > * 1. freer has set numthreads = 0. get() returns 0 > * 2. freer is between lxclock and setting numthreads to 0. get()er will > * sem_wait on privlock, get lxclock after freer() drops it, then see > * numthreads is 0 and exit without touching lxclock again.. > * 3. freer has not yet locked privlock. If get()er runs first, then put()er > * will see --numthreads = 1 and not call lxc_container_free(). > */ > > Signed-off-by: Serge Hallyn <serge.hal...@ubuntu.com>
Acked-by: Seth Arnold <seth.arn...@canonical.com> Thanks
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