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author | Kirill Tkhai <ktkhai@virtuozzo.com> | 2018-04-05 14:58:06 +0300 |
---|---|---|
committer | Jeff Layton <jlayton@redhat.com> | 2018-05-01 14:39:50 +0300 |
commit | 7a107c0f55a3b4c6f84a4323df5610360bde1684 (patch) | |
tree | 776ce70555dbb4714b1ea10f6f10d06a767f0294 /include | |
parent | fff75eb2a08c2ac96404a2d79685668f3cf5a7a3 (diff) | |
download | linux-7a107c0f55a3b4c6f84a4323df5610360bde1684.tar.xz |
fasync: Fix deadlock between task-context and interrupt-context kill_fasync()
I observed the following deadlock between them:
[task 1] [task 2] [task 3]
kill_fasync() mm_update_next_owner() copy_process()
spin_lock_irqsave(&fa->fa_lock) read_lock(&tasklist_lock) write_lock_irq(&tasklist_lock)
send_sigio() <IRQ> ...
read_lock(&fown->lock) kill_fasync() ...
read_lock(&tasklist_lock) spin_lock_irqsave(&fa->fa_lock) ...
Task 1 can't acquire read locked tasklist_lock, since there is
already task 3 expressed its wish to take the lock exclusive.
Task 2 holds the read locked lock, but it can't take the spin lock.
Also, there is possible another deadlock (which I haven't observed):
[task 1] [task 2]
f_getown() kill_fasync()
read_lock(&f_own->lock) spin_lock_irqsave(&fa->fa_lock,)
<IRQ> send_sigio() write_lock_irq(&f_own->lock)
kill_fasync() read_lock(&fown->lock)
spin_lock_irqsave(&fa->fa_lock,)
Actually, we do not need exclusive fa->fa_lock in kill_fasync_rcu(),
as it guarantees fa->fa_file->f_owner integrity only. It may seem,
that it used to give a task a small possibility to receive two sequential
signals, if there are two parallel kill_fasync() callers, and task
handles the first signal fastly, but the behaviour won't become
different, since there is exclusive sighand lock in do_send_sig_info().
The patch converts fa_lock into rwlock_t, and this fixes two above
deadlocks, as rwlock is allowed to be taken from interrupt handler
by qrwlock design.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/fs.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/fs.h b/include/linux/fs.h index 760d8da1b6c7..d6c24b68a092 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1250,7 +1250,7 @@ static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl) } struct fasync_struct { - spinlock_t fa_lock; + rwlock_t fa_lock; int magic; int fa_fd; struct fasync_struct *fa_next; /* singly linked list */ |