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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 /fs | |
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 'fs')
-rw-r--r-- | fs/fcntl.c | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/fs/fcntl.c b/fs/fcntl.c index d737ff082472..c42169459298 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -871,9 +871,9 @@ int fasync_remove_entry(struct file *filp, struct fasync_struct **fapp) if (fa->fa_file != filp) continue; - spin_lock_irq(&fa->fa_lock); + write_lock_irq(&fa->fa_lock); fa->fa_file = NULL; - spin_unlock_irq(&fa->fa_lock); + write_unlock_irq(&fa->fa_lock); *fp = fa->fa_next; call_rcu(&fa->fa_rcu, fasync_free_rcu); @@ -918,13 +918,13 @@ struct fasync_struct *fasync_insert_entry(int fd, struct file *filp, struct fasy if (fa->fa_file != filp) continue; - spin_lock_irq(&fa->fa_lock); + write_lock_irq(&fa->fa_lock); fa->fa_fd = fd; - spin_unlock_irq(&fa->fa_lock); + write_unlock_irq(&fa->fa_lock); goto out; } - spin_lock_init(&new->fa_lock); + rwlock_init(&new->fa_lock); new->magic = FASYNC_MAGIC; new->fa_file = filp; new->fa_fd = fd; @@ -987,14 +987,13 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band) { while (fa) { struct fown_struct *fown; - unsigned long flags; if (fa->magic != FASYNC_MAGIC) { printk(KERN_ERR "kill_fasync: bad magic number in " "fasync_struct!\n"); return; } - spin_lock_irqsave(&fa->fa_lock, flags); + read_lock(&fa->fa_lock); if (fa->fa_file) { fown = &fa->fa_file->f_owner; /* Don't send SIGURG to processes which have not set a @@ -1003,7 +1002,7 @@ static void kill_fasync_rcu(struct fasync_struct *fa, int sig, int band) if (!(sig == SIGURG && fown->signum == 0)) send_sigio(fown, fa->fa_fd, band); } - spin_unlock_irqrestore(&fa->fa_lock, flags); + read_unlock(&fa->fa_lock); fa = rcu_dereference(fa->fa_next); } } |