On Mon, Jan 4, 2021 at 9:28 AM Icenowy Zheng <icenowy@xxxxxxx> wrote: > > 在 2021-01-03星期日的 16:10 +0200，Amir Goldstein写道： > > On Fri, Jan 1, 2021 at 10:12 PM Icenowy Zheng <icenowy@xxxxxxx> > > wrote: > > > > > > The function ovl_dir_real_file() currently uses the semaphore of > > > the > > > inode to synchronize write to the upperfile cache field. > > > > > > However, this function will get called by ovl_ioctl_set_flags(), > > > which > > > utilizes the inode semaphore too. In this case ovl_dir_real_file() > > > will > > > try to claim a lock that is owned by a function in its call stack, > > > which > > > won't get released before ovl_dir_real_file() returns. > > > > oops. I wondered why I didn't see any warnings on this from lockdep. > > Ah! because the xfstest that exercises ovl_ioctl_set_flags() on > > directory, > > generic/079, starts with an already upper dir. > > > > And the xfstest that checks chattr+i on lower/upper files, > > overlay/040, > > does not check chattr on dirs (ioctl on overlay dirs wasn't supported > > at > > the time the test was written). > > > > Would you be able to create a variant of test overlay/040 that also > > tests > > chattr +i on lower/upper dirs to test your patch and confirm that the > > test > > fails on master with the appropriate Kconfig debug options. > > https://gist.github.com/Icenowy/c7d8decb6812d6e5064d143c57281ad3 > > Here's a test that would break on master (I used linux-next/master for > test). Thanks. I am working on another test to improve overlay/030 that may also cover this bug, so maybe no need for both tests. I'll let you know when I'm done. If you like, I can post your test for you with your Signed-of-by if I think it is also needed. > > [ 246.521880] INFO: task chattr:715 blocked for more than 122 seconds. > [ 246.525659] Not tainted 5.11.0-rc1-next-20210104+ #20 > [ 246.528498] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 246.535076] task:chattr state:D stack:13736 pid: 715 ppid: > 529 flags:0x00000000 > [ 246.538923] Call Trace: > [ 246.540241] __schedule+0x2a9/0x820 > [ 246.541986] schedule+0x56/0xc0 > [ 246.543616] rwsem_down_write_slowpath+0x375/0x630 > [ 246.545565] ovl_dir_real_file+0xc1/0x120 > [ 246.547512] ovl_real_fdget+0x35/0x80 > [ 246.549303] ovl_real_ioctl+0x26/0x90 > [ 246.551050] ? mnt_drop_write+0x2c/0x70 > [ 246.553068] ovl_ioctl_set_flags+0x93/0x110 > [ 246.555407] __x64_sys_ioctl+0x7e/0xb0 > [ 246.557175] do_syscall_64+0x33/0x40 > [ 246.558869] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > [ 246.561057] RIP: 0033:0x7fe4a3830b67 > [ 246.565799] RSP: 002b:00007ffe7ad504f8 EFLAGS: 00000246 ORIG_RAX: > 0000000000000010 > [ 246.569438] RAX: ffffffffffffffda RBX: 0000000000000001 RCX: > 00007fe4a3830b67 > [ 246.572061] RDX: 00007ffe7ad5050c RSI: 0000000040086602 RDI: > 0000000000000003 > [ 246.575509] RBP: 0000000000000003 R08: 0000000000000001 R09: > 0000000000000000 > [ 246.578932] R10: 0000000000000000 R11: 0000000000000246 R12: > 0000000000000010 > [ 246.581014] R13: 00007ffe7ad50810 R14: 0000000000000002 R15: > 0000000000000001 > [ 246.582818] > [ 246.582818] Showing all locks held in the system: > [ 246.584741] 1 lock held by khungtaskd/18: > [ 246.586085] #0: ffffffff9e951540 (rcu_read_lock){....}-{1:2}, at: > debug_show_all_locks+0x15/0x100 > [ 246.589775] 3 locks held by chattr/715: > [ 246.591364] #0: ffff96a74b92c450 (sb_writers#11){....}-{0:0}, at: > ovl_ioctl_set_flags+0x2f/0x110 > [ 246.597182] #1: ffff96a7489c3500 > (&ovl_i_mutex_dir_key[depth]){....}-{3:3}, at: > ovl_ioctl_set_flags+0x54/0x110 > [ 246.601325] #2: ffff96a7489c3500 > (&ovl_i_mutex_dir_key[depth]){....}-{3:3}, at: > ovl_dir_real_file+0xc1/0x120 > > > > > > > > > Define a dedicated semaphore for the upperfile cache, so that the > > > deadlock won't happen. > > > > > > Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and FS[S|G]ETXATTR > > > ioctls for directories") > > > Cc: stable@xxxxxxxxxxxxxxx # v5.10 > > > Signed-off-by: Icenowy Zheng <icenowy@xxxxxxx> > > > --- > > > fs/overlayfs/readdir.c | 6 ++++-- > > > 1 file changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c > > > index 01620ebae1bd..f10701aabb71 100644 > > > --- a/fs/overlayfs/readdir.c > > > +++ b/fs/overlayfs/readdir.c > > > @@ -56,6 +56,7 @@ struct ovl_dir_file { > > > struct list_head *cursor; > > > struct file *realfile; > > > struct file *upperfile; > > > + struct semaphore upperfile_sem; > > > > mutex please > > You missed this comment. semaphore is discouraged as a locking primitive. Please use struct mutex. Thanks, Amir.
