user/sven/linux.git/drivers/tty/tty_ldsem.c, branch v4.4.283

tty/ldsem, locking/rwsem: Add missing ACQUIRE to read_failed sleep loop

2019-08-25T08:52:51Z

[ Upstream commit 952041a8639a7a3a73a2b6573cb8aa8518bc39f8 ] While reviewing rwsem down_slowpath, Will noticed ldsem had a copy of a bug we just found for rwsem. X = 0; CPU0 CPU1 rwsem_down_read() for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); X = 1; rwsem_up_write(); rwsem_mark_wake() atomic_long_add(adjustment, &sem->count); smp_store_release(&waiter->task, NULL); if (!waiter.task) break; ... } r = X; Allows 'r == 0'. Reported-by: Will Deacon Signed-off-by: Peter Zijlstra (Intel) Acked-by: Will Deacon Cc: Linus Torvalds Cc: Peter Hurley Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 4898e640caf0 ("tty: Add timed, writer-prioritized rw semaphore") Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

tty/ldsem: Wake up readers after timed out down_write()

2019-01-26T08:42:45Z

commit 231f8fd0cca078bd4396dd7e380db813ac5736e2 upstream. ldsem_down_read() will sleep if there is pending writer in the queue. If the writer times out, readers in the queue should be woken up, otherwise they may miss a chance to acquire the semaphore until the last active reader will do ldsem_up_read(). There was a couple of reports where there was one active reader and other readers soft locked up: Showing all locks held in the system: 2 locks held by khungtaskd/17: #0: (rcu_read_lock){......}, at: watchdog+0x124/0x6d1 #1: (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3 2 locks held by askfirst/123: #0: (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58 #1: (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4 Prevent readers wait for active readers to release ldisc semaphore. Link: lkml.kernel.org/r/20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com Link: lkml.kernel.org/r/20180907045041.GF1110@shao2-debian Cc: Jiri Slaby Cc: Peter Zijlstra Cc: stable@vger.kernel.org Reported-by: kernel test robot Signed-off-by: Dmitry Safonov Signed-off-by: Greg Kroah-Hartman

tty: tty_ldsem.c: move assignment out of if () block

2015-05-10T17:04:18Z

We should not be doing assignments within an if () block so fix up the code to not do this. change was created using Coccinelle. CC: Jiri Slaby Signed-off-by: Greg Kroah-Hartman

lockdep: Make held_lock->check and "int check" argument bool

2014-02-09T20:18:54Z

The "int check" argument of lock_acquire() and held_lock->check are misleading. This is actually a boolean: 2 means "true", everything else is "false". And there is no need to pass 1 or 0 to lock_acquire() depending on CONFIG_PROVE_LOCKING, __lock_acquire() checks prove_locking at the start and clears "check" if !CONFIG_PROVE_LOCKING. Note: probably we can simply kill this member/arg. The only explicit user of check => 0 is rcu_lock_acquire(), perhaps we can change it to use lock_acquire(trylock =>, read => 2). __lockdep_no_validate means check => 0 implicitly, but we can change validate_chain() to check hlock->instance->key instead. Not to mention it would be nice to get rid of lockdep_set_novalidate_class(). Signed-off-by: Oleg Nesterov Cc: Dave Jones Cc: Greg Kroah-Hartman Cc: Linus Torvalds Cc: Paul McKenney Cc: Steven Rostedt Cc: Alan Stern Cc: Sasha Levin Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20140120182006.GA26495@redhat.com Signed-off-by: Ingo Molnar

tty: Fix hang at ldsem_down_read()

2013-12-17T00:55:43Z

When a controlling tty is being hung up and the hang up is waiting for a just-signalled tty reader or writer to exit, and a new tty reader/writer tries to acquire an ldisc reference concurrently with the ldisc reference release from the signalled reader/writer, the hangup can hang. The new reader/writer is sleeping in ldsem_down_read() and the hangup is sleeping in ldsem_down_write() [1]. The new reader/writer fails to wakeup the waiting hangup because the wrong lock count value is checked (the old lock count rather than the new lock count) to see if the lock is unowned. Change helper function to return the new lock count if the cmpxchg was successful; document this behavior. [1] edited dmesg log from reporter SysRq : Show Blocked State task PC stack pid father systemd D ffff88040c4f0000 0 1 0 0x00000000 ffff88040c49fbe0 0000000000000046 ffff88040c4a0000 ffff88040c49ffd8 00000000001d3980 00000000001d3980 ffff88040c4a0000 ffff88040593d840 ffff88040c49fb40 ffffffff810a4cc0 0000000000000006 0000000000000023 Call Trace: [] ? sched_clock_cpu+0x9f/0xe4 [] ? sched_clock_cpu+0x9f/0xe4 [] ? sched_clock_cpu+0x9f/0xe4 [] ? sched_clock_cpu+0x9f/0xe4 [] schedule+0x24/0x5e [] schedule_timeout+0x15b/0x1ec [] ? sched_clock_cpu+0x9f/0xe4 [] ? _raw_spin_unlock_irq+0x24/0x26 [] down_read_failed+0xe3/0x1b9 [] ldsem_down_read+0x8b/0xa5 [] ? tty_ldisc_ref_wait+0x1b/0x44 [] tty_ldisc_ref_wait+0x1b/0x44 [] tty_write+0x7d/0x28a [] redirected_tty_write+0x8d/0x98 [] ? tty_write+0x28a/0x28a [] do_loop_readv_writev+0x56/0x79 [] do_readv_writev+0x1b0/0x1ff [] ? do_vfs_ioctl+0x32a/0x489 [] ? final_putname+0x1d/0x3a [] vfs_writev+0x2e/0x49 [] SyS_writev+0x47/0xaa [] system_call_fastpath+0x16/0x1b bash D ffffffff81c104c0 0 5469 5302 0x00000082 ffff8800cf817ac0 0000000000000046 ffff8804086b22a0 ffff8800cf817fd8 00000000001d3980 00000000001d3980 ffff8804086b22a0 ffff8800cf817a48 000000000000b9a0 ffff8800cf817a78 ffffffff81004675 ffff8800cf817a44 Call Trace: [] ? dump_trace+0x165/0x29c [] ? sched_clock_cpu+0x9f/0xe4 [] ? save_stack_trace+0x26/0x41 [] schedule+0x24/0x5e [] schedule_timeout+0x15b/0x1ec [] ? sched_clock_cpu+0x9f/0xe4 [] ? down_write_failed+0xa3/0x1c9 [] ? _raw_spin_unlock_irq+0x24/0x26 [] down_write_failed+0xab/0x1c9 [] ldsem_down_write+0x79/0xb1 [] ? tty_ldisc_lock_pair_timeout+0xa5/0xd9 [] tty_ldisc_lock_pair_timeout+0xa5/0xd9 [] tty_ldisc_hangup+0xc4/0x218 [] __tty_hangup+0x2e2/0x3ed [] disassociate_ctty+0x63/0x226 [] do_exit+0x79f/0xa11 [] ? get_signal_to_deliver+0x206/0x62f [] ? lock_release_holdtime.part.8+0xf/0x16e [] do_group_exit+0x47/0xb5 [] get_signal_to_deliver+0x241/0x62f [] do_signal+0x43/0x59d [] ? __audit_syscall_exit+0x21a/0x2a8 [] ? lock_release_holdtime.part.8+0xf/0x16e [] do_notify_resume+0x54/0x6c [] int_signal+0x12/0x17 Reported-by: Sami Farin Cc: # 3.12.x Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Add timed, writer-prioritized rw semaphore

2013-05-20T19:30:32Z

The semantics of a rw semaphore are almost ideally suited for tty line discipline lifetime management; multiple active threads obtain "references" (read locks) while performing i/o to prevent the loss or change of the current line discipline (write lock). Unfortunately, the existing rw_semaphore is ill-suited in other ways; 1) TIOCSETD ioctl (change line discipline) expects to return an error if the line discipline cannot be exclusively locked within 5 secs. Lock wait timeouts are not supported by rwsem. 2) A tty hangup is expected to halt and scrap pending i/o, so exclusive locking must be prioritized. Writer priority is not supported by rwsem. Add ld_semaphore which implements these requirements in a semantically similar way to rw_semaphore. Writer priority is handled by separate wait lists for readers and writers. Pending write waits are priortized before existing read waits and prevent further read locks. Wait timeouts are trivially added, but obviously change the lock semantics as lock attempts can fail (but only due to timeout). This implementation incorporates the write-lock stealing work of Michel Lespinasse . Cc: Michel Lespinasse Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman