Herbert applied this to his tree. It's probably a good stable candidate, since it's a two line change to fix a race condition. On Fri, Mar 24, 2017 at 3:16 PM, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote: > Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: >> Under extremely heavy uses of padata, crashes occur, and with list >> debugging turned on, this happens instead: >> >> [87487.298728] WARNING: CPU: 1 PID: 882 at lib/list_debug.c:33 >> __list_add+0xae/0x130 >> [87487.301868] list_add corruption. prev->next should be next >> (ffffb17abfc043d0), but was ffff8dba70872c80. (prev=ffff8dba70872b00). >> [87487.339011] [<ffffffff9a53d075>] dump_stack+0x68/0xa3 >> [87487.342198] [<ffffffff99e119a1>] ? console_unlock+0x281/0x6d0 >> [87487.345364] [<ffffffff99d6b91f>] __warn+0xff/0x140 >> [87487.348513] [<ffffffff99d6b9aa>] warn_slowpath_fmt+0x4a/0x50 >> [87487.351659] [<ffffffff9a58b5de>] __list_add+0xae/0x130 >> [87487.354772] [<ffffffff9add5094>] ? _raw_spin_lock+0x64/0x70 >> [87487.357915] [<ffffffff99eefd66>] padata_reorder+0x1e6/0x420 >> [87487.361084] [<ffffffff99ef0055>] padata_do_serial+0xa5/0x120 >> >> padata_reorder calls list_add_tail with the list to which its adding >> locked, which seems correct: >> >> spin_lock(&squeue->serial.lock); >> list_add_tail(&padata->list, &squeue->serial.list); >> spin_unlock(&squeue->serial.lock); >> >> This therefore leaves only place where such inconsistency could occur: >> if padata->list is added at the same time on two different threads. >> This pdata pointer comes from the function call to >> padata_get_next(pd), which has in it the following block: >> >> next_queue = per_cpu_ptr(pd->pqueue, cpu); >> padata = NULL; >> reorder = &next_queue->reorder; >> if (!list_empty(&reorder->list)) { >> padata = list_entry(reorder->list.next, >> struct padata_priv, list); >> spin_lock(&reorder->lock); >> list_del_init(&padata->list); >> atomic_dec(&pd->reorder_objects); >> spin_unlock(&reorder->lock); >> >> pd->processed++; >> >> goto out; >> } >> out: >> return padata; >> >> I strongly suspect that the problem here is that two threads can race >> on reorder list. Even though the deletion is locked, call to >> list_entry is not locked, which means it's feasible that two threads >> pick up the same padata object and subsequently call list_add_tail on >> them at the same time. The fix is thus be hoist that lock outside of >> that block. >> >> Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> > > Patch applied. Thanks. > -- > Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt