Messages in this thread Patch in this message | | | From | Nick Piggin <> | Subject | Re: [2.6.27-rc5] inotify_read's ev_mutex vs do_page_fault's mmap_sem... | Date | Thu, 11 Sep 2008 06:12:51 +1000 |
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On Wednesday 10 September 2008 14:07, Nick Piggin wrote: > On Wednesday 10 September 2008 07:03, Daniel J Blueman wrote: > > I observed this locking violation [1] while gnome-panel was loading; > > this was previously reported at > > http://uwsg.iu.edu/hypermail/linux/kernel/0806.3/2881.html . > > > > Let me know for more information/config/testing. Thanks! > > Thanks for the report. I've attached a patch you could test. It compiles > (and boots a UML here) but I don't think I've actually tested the inotify > path at all, so it may explode on you.
Indeed it was wrong, I messed up the waitqueue handling. This one survives longer for me... Fix inotify lock order reversal with mmap_sem due to holding locks over copy_to_user.
Signed-off-by: Nick Piggin <npiggin@suse.de> --- Index: linux-2.6/fs/inotify_user.c =================================================================== --- linux-2.6.orig/fs/inotify_user.c +++ linux-2.6/fs/inotify_user.c @@ -323,7 +323,7 @@ out: } /* - * remove_kevent - cleans up and ultimately frees the given kevent + * remove_kevent - cleans up the given kevent * * Caller must hold dev->ev_mutex. */ @@ -334,7 +334,13 @@ static void remove_kevent(struct inotify dev->event_count--; dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len; +} +/* + * free_kevent - frees the given kevent. + */ +static void free_kevent(struct inotify_kernel_event *kevent) +{ kfree(kevent->name); kmem_cache_free(event_cachep, kevent); } @@ -350,6 +356,7 @@ static void inotify_dev_event_dequeue(st struct inotify_kernel_event *kevent; kevent = inotify_dev_get_event(dev); remove_kevent(dev, kevent); + free_kevent(kevent); } } @@ -433,17 +440,15 @@ static ssize_t inotify_read(struct file dev = file->private_data; while (1) { - int events; prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE); mutex_lock(&dev->ev_mutex); - events = !list_empty(&dev->events); - mutex_unlock(&dev->ev_mutex); - if (events) { + if (!list_empty(&dev->events)) { ret = 0; break; } + mutex_unlock(&dev->ev_mutex); if (file->f_flags & O_NONBLOCK) { ret = -EAGAIN; @@ -462,7 +467,6 @@ static ssize_t inotify_read(struct file if (ret) return ret; - mutex_lock(&dev->ev_mutex); while (1) { struct inotify_kernel_event *kevent; @@ -481,6 +485,13 @@ static ssize_t inotify_read(struct file } break; } + remove_kevent(dev, kevent); + + /* + * Must perform the copy_to_user outside the mutex in order + * to avoid a lock order reversal with mmap_sem. + */ + mutex_unlock(&dev->ev_mutex); if (copy_to_user(buf, &kevent->event, event_size)) { ret = -EFAULT; @@ -498,7 +509,9 @@ static ssize_t inotify_read(struct file count -= kevent->event.len; } - remove_kevent(dev, kevent); + free_kevent(kevent); + + mutex_lock(&dev->ev_mutex); } mutex_unlock(&dev->ev_mutex); Index: linux-2.6/include/asm-x86/uaccess_64.h =================================================================== --- linux-2.6.orig/include/asm-x86/uaccess_64.h +++ linux-2.6/include/asm-x86/uaccess_64.h @@ -7,6 +7,7 @@ #include <linux/compiler.h> #include <linux/errno.h> #include <linux/prefetch.h> +#include <linux/lockdep.h> #include <asm/page.h> /* | |