Messages in this thread Patch in this message | | | Subject | Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5 | From | Thomas Gleixner <> | Date | Tue, 19 Oct 2004 10:09:25 +0200 |
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On Mon, 2004-10-18 at 16:50, Ingo Molnar wrote: > i have released the -U5 Real-Time Preemption patch: >
starting nfsd triggers the deadlock detection, but it's not really a deadlock.
The first nfsd thread acquires nlmsvc_sema. The other 7 nfsd threads wait on it. The first thread creates lockd and tries to get lockd_start, which is initialized locked and will be released when the lockd thread starts. The deadlock complains about a deadlock on nlmsvc_sema inside of down(&lockd_start). ?
Converting lockd_start to a waitqueue solves the problem and is more sane, than the locked mutex.
tglx
--- 2.6.9-rc4-mm1-RT-U5/fs/lockd/svc.c.orig 2004-10-19 10:02:17.000000000 +0200 +++ 2.6.9-rc4-mm1-RT-U5/fs/lockd/svc.c 2004-10-19 09:54:22.000000000 +0200 @@ -46,7 +46,7 @@ int nlmsvc_grace_period; unsigned long nlmsvc_timeout;
-static DECLARE_MUTEX(lockd_start); +static DECLARE_WAIT_QUEUE_HEAD(lockd_start); static DECLARE_WAIT_QUEUE_HEAD(lockd_exit);
/* @@ -109,7 +109,7 @@ * Let our maker know we're running. */ nlmsvc_pid = current->pid; - up(&lockd_start); + wake_up(&lockd_start);
daemonize("lockd");
@@ -230,6 +230,7 @@ printk(KERN_WARNING "lockd_up: no pid, %d users??\n", nlmsvc_users);
+ error = -ENOMEM; serv = svc_create(&nlmsvc_program, LOCKD_BUFSIZE); if (!serv) { @@ -258,7 +259,19 @@ "lockd_up: create thread failed, error=%d\n", error); goto destroy_and_out; } - down(&lockd_start); + /* + * Wait for the lockd process to start, but since we're holding + * the lockd semaphore, we can't wait around forever ... + */ + clear_thread_flag(TIF_SIGPENDING); + interruptible_sleep_on_timeout(&lockd_start, HZ); + if (!nlmsvc_pid) { + printk(KERN_WARNING + "lockd_down: lockd failed to start\n"); + } + spin_lock_irq(¤t->sighand->siglock); + recalc_sigpending(); + spin_unlock_irq(¤t->sighand->siglock);
/* * Note: svc_serv structures have an initial use count of 1, @@ -423,7 +436,6 @@
static int __init init_nlm(void) { - init_MUTEX_LOCKED(&lockd_start); nlm_sysctl_table = register_sysctl_table(nlm_sysctl_root, 0); return nlm_sysctl_table ? 0 : -ENOMEM; }
Installing knfsd (copyright (C) 1996 okir@monad.swb.de). mountdBUG: semaphore deadlock detected! .. task nfsd/1246 is holding c89f4560. 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 Call Trace: [<c0117fc7>] copy_process+0x5f7/0xc30 [<c01c4e62>] __delay+0x12/0x20 [<c01fe460>] serial8250_console_write+0x170/0x280 [<c011930e>] __call_console_drivers+0x5e/0x60 [<c011982a>] release_console_sem+0xda/0xe0 [<c01196a7>] vprintk+0x107/0x160 [<c01196a7>] vprintk+0x107/0x160 [<c012a3ae>] __kernel_text_address+0x2e/0x40 [<c0106bf5>] show_trace+0x35/0x90 [<c0106bf5>] show_trace+0x35/0x90 [<c0106cd0>] show_stack+0x80/0xa0 [<c01c2976>] __rwsem_deadlock+0x136/0x180 [<c01c28aa>] __rwsem_deadlock+0x6a/0x180 [<c02c3c33>] __down_write+0x93/0x170 [<c01c3033>] down_write+0x43/0x80 [<c89e661d>] lockd_up+0x9d/0x120 [lockd] [<c89e62e0>] lockd+0x0/0x2a0 [lockd] [<c883d2e1>] nfsd+0x91/0x380 [nfsd] [<c0105e12>] ret_from_fork+0x6/0x14 [<c883d250>] nfsd+0x0/0x380 [nfsd] [<c0103ffd>] kernel_thread_helper+0x5/0x18 ...#0 task nfsd/1246 is holding c89f4560. BUG: semaphore deadlock: nfsd/1252 is blocked on c89f4560, deadlocking nfsd/1246 c733df60 00000046 c7adad10 c03d6060 00000000 00000000 00000000 00000000 00000000 00000000 c7a306f0 00005b6e 39133ac7 0000001a c7adae6c c7adad10 c7adad10 c7584400 00000000 c02c3cad c89f4560 c6853f6c c6819f6c c7adad10 Call Trace: [<c02c3cad>] __down_write+0x10d/0x170 [<c01c3033>] down_write+0x43/0x80 [<c89e6591>] lockd_up+0x11/0x120 [lockd] [<c883d250>] nfsd+0x0/0x380 [nfsd] [<c883d2e1>] nfsd+0x91/0x380 [nfsd] [<c0105e12>] ret_from_fork+0x6/0x14 [<c883d250>] nfsd+0x0/0x380 [nfsd] [<c0103ffd>] kernel_thread_helper+0x5/0x18 ------------[ cut here ]------------
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