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| author | Keir Fraser <keir.fraser@citrix.com> | 2010-04-15 11:33:39 +0100 |
|---|---|---|
| committer | Keir Fraser <keir.fraser@citrix.com> | 2010-04-15 11:33:39 +0100 |
| commit | 86cd882200f54655c553c40341cd8ab3ecf378ad (patch) | |
| tree | 2386ccfe170580b1af61061f05cb44d47ff5610f /xen/common/sysctl.c | |
| parent | dcc9060e4a4a7bb6287ca346580529c8d803c780 (diff) | |
| download | xen-86cd882200f54655c553c40341cd8ab3ecf378ad.tar.gz xen-86cd882200f54655c553c40341cd8ab3ecf378ad.tar.bz2 xen-86cd882200f54655c553c40341cd8ab3ecf378ad.zip | |
Update comments around spin_trylock() usage for sysctl and xenpf locks.
Since the execution of stop_machine_run() via cpu_down() is now always
deferred to a hypercall continuation context, the above locks are not
held at that time. Hence the trylock is not specifically to avoid
deadlock with stop_machine_run(), but rather a more general paranoia
about deadlocks in general.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
Diffstat (limited to 'xen/common/sysctl.c')
| -rw-r--r-- | xen/common/sysctl.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/xen/common/sysctl.c b/xen/common/sysctl.c index ba16353266..db27fc233c 100644 --- a/xen/common/sysctl.c +++ b/xen/common/sysctl.c @@ -48,7 +48,11 @@ long do_sysctl(XEN_GUEST_HANDLE(xen_sysctl_t) u_sysctl) if ( op->interface_version != XEN_SYSCTL_INTERFACE_VERSION ) return -EACCES; - /* spin_trylock() avoids deadlock with stop_machine_run(). */ + /* + * Trylock here avoids deadlock with an existing sysctl critical section + * which might (for some current or future reason) want to synchronise + * with this vcpu. + */ while ( !spin_trylock(&sysctl_lock) ) if ( hypercall_preempt_check() ) return hypercall_create_continuation( |