[PATCH] Reduce uidhash lock hold time when lookup succeeds
When lookup succeeds we don't need the "new" user struct which hasn't been linked into the uidhash. So we can immediately drop the lock and then free "new" rather than free it with the lock held. Signed-off-by: Matt Helsley <matthltc@us.ibm.com> Cc: David Howells <dhowells@redhat.com> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: "Serge E. Hallyn" <serge@hallyn.com> Cc: containers@lists.linux-foundation.org --- kernel/user.c | 12 +++++++----- 1 files changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/user.c b/kernel/user.c index 5c598ca..4ea8e58 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -157,16 +157,18 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) */ spin_lock_irq(&uidhash_lock); up = uid_hash_find(uid, hashent); - if (up) { + if (!up) { + uid_hash_insert(new, hashent); + up = new; + } + spin_unlock_irq(&uidhash_lock); + + if (up != new) { put_user_ns(ns); key_put(new->uid_keyring); key_put(new->session_keyring); kmem_cache_free(uid_cachep, new); - } else { - uid_hash_insert(new, hashent); - up = new; } - spin_unlock_irq(&uidhash_lock); } return up; -- 1.6.3.3 _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/containe rs
Re: [PATCH] Reduce uidhash lock hold time when lookup succeeds
Quoting Matt Helsley (matthltc@us.ibm.com): > When lookup succeeds we don't need the "new" user struct which hasn't > been linked into the uidhash. So we can immediately drop the lock and > then free "new" rather than free it with the lock held. > > Signed-off-by: Matt Helsley <matthltc@us.ibm.com> > Cc: David Howells <dhowells@redhat.com> > Cc: Pavel Emelyanov <xemul@parallels.com> > Cc: Alexey Dobriyan <adobriyan@gmail.com> > Cc: "Serge E. Hallyn" <serge@hallyn.com> Acked-by: Serge E. Hallyn <serge@hallyn.com> And might I say that the label 'out_unlock' in that function is sadly named :) > Cc: containers@lists.linux-foundation.org > --- > kernel/user.c | 12 +++++++----- > 1 files changed, 7 insertions(+), 5 deletions(-) > > diff --git a/kernel/user.c b/kernel/user.c > index 5c598ca..4ea8e58 100644 > --- a/kernel/user.c > +++ b/kernel/user.c > @@ -157,16 +157,18 @@ struct user_struct *alloc_uid(struct user_namespace *ns, uid_t uid) > */ > spin_lock_irq(&uidhash_lock); > up = uid_hash_find(uid, hashent); > - if (up) { > + if (!up) { > + uid_hash_insert(new, hashent); > + up = new; > + } > + spin_unlock_irq(&uidhash_lock); > + > + if (up != new) { > put_user_ns(ns); > key_put(new->uid_keyring); > key_put(new->session_keyring); > kmem_cache_free(uid_cachep, new); > - } else { > - uid_hash_insert(new, hashent); > - up = new; > } > - spin_unlock_irq(&uidhash_lock); > } > > return up; > -- > 1.6.3.3 > > _______________________________________________ > Containers mailing list > Containers@lists.linux-foundation.org > https://lists.linux-foundation.org/mailman/listinfo/containe rs _______________________________________________ Containers mailing list Containers@lists.linux-foundation.org https://lists.linux-foundation.org/mailman/listinfo/containe rs