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scst_main: Fix race between scst_resume_activity() and scst_init_thread()

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After SCST_FLAG_SUSPENDED has been cleared it is essential that
scst_do_job_init() reexamines scst_init_cmd_list to avoid that
commands get stuck in the command init list. This patch fixes the
following race condition that can occur if SCST_FLAG_SUSPENDED
has been set and if scst_init_cmd_list is not empty:
* scst_do_job_init() returns to scst_init_thread() and leaves the
  commands that were on the init list on that list.
* scst_init_thread() invokes test_init_cmd_list().
* test_init_cmd_list() returns false because SCST_FLAG_SUSPENDED
  has been set.
* scst_resume_activity() clears SCST_FLAG_SUSPENDED and invokes
  wake_up_all(&scst_init_cmd_list_waitQ). However, since
  scst_init_thread() has not yet added the init thread back to
  scst_init_cmd_list_waitQ this wake_up_all() call doesn't do
  anything.
* scst_init_thread() adds the init thread to scst_init_cmd_list_waitQ
  and unlocks scst_init_lock.

Additionally, remove an unneeded smp_mb__after_clear_bit() call.
wake_up_all() guarantees that if it wakes up a thread that that
thread sees all store operations that were performed by the thread
that invoked wake_up_all() and that preceeded the wake_up_all()
invocation.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>



git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@5524 d57e44dd-8a1f-0410-8b47-8ef2f437770f
This commit is contained in:
Vladislav Bolkhovitin
2014-05-17 01:04:08 +00:00
parent 0bf5a3ca92
commit b39b5d8502
2 changed files with 8 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
scst/src/scst_main.c
View File

@@ -1060,17 +1060,20 @@ static void __scst_resume_activity(void)
goto out;
clear_bit(SCST_FLAG_SUSPENDED, &scst_flags);
/*
* The barrier is needed to make sure all woken up threads see the
* cleared flag. Not sure if it's really needed, but let's be safe.
*/
smp_mb__after_clear_bit();
mutex_lock(&scst_cmd_threads_mutex);
list_for_each_entry(l, &scst_cmd_threads_list, lists_list_entry) {
wake_up_all(&l->cmd_list_waitQ);
}
mutex_unlock(&scst_cmd_threads_mutex);
/*
* Wait until scst_init_thread() either is waiting or has reexamined
* scst_flags.
*/
spin_lock_irq(&scst_init_lock);
spin_unlock_irq(&scst_init_lock);
wake_up_all(&scst_init_cmd_list_waitQ);
spin_lock_irq(&scst_mcmd_lock);

4
scst/src/scst_targ.c
View File

@@ -4547,10 +4547,6 @@ restart:
goto restart;
}
/* It isn't really needed, but let's keep it */
if (susp != test_bit(SCST_FLAG_SUSPENDED, &scst_flags))
goto restart;
TRACE_EXIT();
return;
}