On Thu, Apr 25, 2013 at 1:38 AM, Davidlohr Bueso <davidlohr.bueso@xxxxxx> wrote: > 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 :) > No, I am not of those "bad guys" in OSS. I would not have invested so much time in helping to get this fixed. Did my usual test-case: A kernel-rebuild within same kernel-environment with no breakage or abnormalities in the logs. Hope I could help. - Sedat - > 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
