On Thu, 2013-04-25 at 01:05 +0200, Sedat Dilek wrote: > On Thu, Apr 25, 2013 at 12:16 AM, Davidlohr Bueso > <davidlohr.bueso@xxxxxx> wrote: > > From: Davidlohr Bueso <davidlohr.bueso@xxxxxx> > > > > Sedat reported an issue leading to a NULL dereference in update_queue(): > > > > [ 178.490583] BUG: spinlock bad magic on CPU#1, sh/8066 > > [ 178.490595] lock: 0xffff88008b53ea18, .magic: 6b6b6b6b, .owner: make/8068, .owner_cpu: 3 > > [ 178.490599] BUG: unable to handle kernel NULL pointer dereference at (null) > > [ 178.490608] IP: [<ffffffff812bacd0>] update_queue+0x70/0x210 > > [ 178.490610] PGD 0 > > [ 178.490612] Oops: 0000 [#1] SMP > > ... > > [ 178.490704] Call Trace: > > [ 178.490710] [<ffffffff812baf51>] do_smart_update+0xe1/0x140 > > [ 178.490713] [<ffffffff812bd6e1>] exit_sem+0x2b1/0x350 > > [ 178.490718] [<ffffffff8105de80>] do_exit+0x290/0xa70 > > [ 178.490721] [<ffffffff8105e6f4>] do_group_exit+0x44/0xa0 > > [ 178.490724] [<ffffffff8105e767>] SyS_exit_group+0x17/0x20 > > [ 178.490728] [<ffffffff816ce15d>] system_call_fastpath+0x1a/0x1f > > > > Linus pin-pointed the problem to a race in the reference counter. To quote: > > > > "That dmesg spew very much implies that the same RCU head got added twice to the RCU > > freeing list, and the only way that happens is if the refcount goes to > > zero twice. Which implies that either we increment a zero, or we lack > > locking and the coherency of the non-atomic access goes away." > > > > This patch converts the IPC RCU header's reference counter to atomic_t. The return of > > ipc_rcu_getref() is modified to inform the callers if it actually succeeded. > > > > Now all callers return -EIDRM upon failure and abort the current operation. Two exceptions are > > in semaphore code where sem_getref_and_unlock() and sem_getref() trigger a warning but proceed > > to freeing up any held locks. > > > > Signed-off-by: Davidlohr Bueso <davidlohr.bueso@xxxxxx> > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > CC: Rik van Riel <riel@xxxxxxxxxxx> > > CC: Paul McKenney <paul.mckenney@xxxxxxxxxx> > > CC: Sedat Dilek <sedat.dilek@xxxxxxxxx> > > CC: Emmanuel Benisty <benisty.e@xxxxxxxxx> > > CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Missing my Reported-by ...! Not trying to take away credit or efforts from you, just wanted you to reconfirm that *this* actual patch fixes things for you :) Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
