Hi !
I was playing with nbd on some little ARM bmc here with lockdep enabled and I
get the following report. I don't have the bandwidth to dig into it this week
to check if it's a false positive so I'm posting it here instead.
Cheers,
Ben.
# nbd-client pasglop /dev/nbd0
Warning: the oldstyle protocol is no longer supported.
This method now uses the newstyle protocol with a default export
Negotiation: ..size = 1431MB
bs=1024, sz=1501[ 518.762967]
[ 518.765614] ======================================================
[ 518.771800] WARNING: possible circular locking dependency detected
[ 518.777983] 4.16.0-00009-ga7c2ef9375ca #240 Not tainted
[ 518.783212] ------------------------------------------------------
[ 518.789393] nbd-client/586 is trying to acquire lock:
[ 518.794446] (&bdev->bd_mutex){+.+.}, at: [<d2ad63df>] blkdev_reread_part+0x18/0x34
[ 518.802185]
[ 518.802185] but task is already holding lock:
[ 518.808024] (&nbd->config_lock){+.+.}, at: [<67337fb4>] nbd_ioctl+0x50/0x35c
[ 518.815210]
[ 518.815210] which lock already depends on the new lock.
[ 518.815210]
[ 518.823389]
[ 518.823389] the existing dependency chain (in reverse order) is:
[ 518.830867]
[ 518.830867] -> #2 (&nbd->config_lock){+.+.}:
[ 518.836655] mutex_lock_nested+0x1c/0x24
[ 518.841110] nbd_open+0x70/0xd8
[ 518.844792] __blkdev_get+0xa0/0x3f4
[ 518.848896] blkdev_get+0x13c/0x358
[ 518.852933] do_dentry_open.constprop.4+0x124/0x308
[ 518.858347] path_openat+0x554/0x1168
[ 518.862536] do_filp_open+0x60/0xc4
[ 518.866556] do_sys_open+0x14c/0x1e8
[ 518.870657] ret_fast_syscall+0x0/0x28
[ 518.874936] 0x7ef7c980
[ 518.877903]
[ 518.877903] -> #1 (nbd_index_mutex){+.+.}:
[ 518.883517] mutex_lock_nested+0x1c/0x24
[ 518.887980] nbd_open+0x14/0xd8
[ 518.891662] __blkdev_get+0xa0/0x3f4
[ 518.895764] blkdev_get+0x13c/0x358
[ 518.899795] do_dentry_open.constprop.4+0x124/0x308
[ 518.905204] path_openat+0x554/0x1168
[ 518.909394] do_filp_open+0x60/0xc4
[ 518.913407] do_sys_open+0x14c/0x1e8
[ 518.917508] ret_fast_syscall+0x0/0x28
[ 518.921785] 0x7ef7c980
[ 518.924755]
[ 518.924755] -> #0 (&bdev->bd_mutex){+.+.}:
[ 518.930368] __mutex_lock+0x74/0x638
[ 518.934470] mutex_lock_nested+0x1c/0x24
[ 518.938938] blkdev_reread_part+0x18/0x34
[ 518.943490] nbd_ioctl+0x2d0/0x35c
[ 518.947425] blkdev_ioctl+0x5a4/0xb18
[ 518.951626] do_vfs_ioctl+0x8c/0x7cc
[ 518.955727] SyS_ioctl+0x34/0x58
[ 518.959490] ret_fast_syscall+0x0/0x28
[ 518.963767] 0x7ef7c984
[ 518.966736]
[ 518.966736] other info that might help us debug this:
[ 518.966736]
[ 518.974734] Chain exists of:
[ 518.974734] &bdev->bd_mutex --> nbd_index_mutex --> &nbd->config_lock
[ 518.974734]
[ 518.985715] Possible unsafe locking scenario:
[ 518.985715]
[ 518.991634] CPU0 CPU1
[ 518.996157] ---- ----
[ 519.000681] lock(&nbd->config_lock);
[ 519.004443] lock(nbd_index_mutex);
[ 519.010544] lock(&nbd->config_lock);
[ 519.016810] lock(&bdev->bd_mutex);
[ 519.020399]
[ 519.020399] *** DEADLOCK ***
[ 519.020399]
[ 519.026323] 1 lock held by nbd-client/586:
[ 519.030419] #0: (&nbd->config_lock){+.+.}, at: [<67337fb4>] nbd_ioctl+0x50/0x35c
[ 519.038030]
[ 519.038030] stack backtrace:
[ 519.042397] CPU: 0 PID: 586 Comm: nbd-client Not tainted 4.16.0-00009-ga7c2ef9375ca #240
[ 519.050484] Hardware name: Generic DT based system
[ 519.055328] [<8000ff20>] (unwind_backtrace) from [<8000da4c>] (show_stack+0x10/0x14)
[ 519.063110] [<8000da4c>] (show_stack) from [<8004bbf4>] (print_circular_bug.constprop.19+0x264/0x2bc)
[ 519.072348] [<8004bbf4>] (print_circular_bug.constprop.19) from [<8004a2ec>] (__lock_acquire+0x14f0/0x18d0)
[ 519.082101] [<8004a2ec>] (__lock_acquire) from [<8004ae30>] (lock_acquire+0x68/0x88)
[ 519.089866] [<8004ae30>] (lock_acquire) from [<8044db04>] (__mutex_lock+0x74/0x638)
[ 519.097540] [<8044db04>] (__mutex_lock) from [<8044e0e4>] (mutex_lock_nested+0x1c/0x24)
[ 519.105576] [<8044e0e4>] (mutex_lock_nested) from [<801d1c70>] (blkdev_reread_part+0x18/0x34)
[ 519.114129] [<801d1c70>] (blkdev_reread_part) from [<802abd44>] (nbd_ioctl+0x2d0/0x35c)
[ 519.122152] [<802abd44>] (nbd_ioctl) from [<801d2a88>] (blkdev_ioctl+0x5a4/0xb18)
[ 519.129655] [<801d2a88>] (blkdev_ioctl) from [<800f3c40>] (do_vfs_ioctl+0x8c/0x7cc)
[ 519.137325] [<800f3c40>] (do_vfs_ioctl) from [<800f43b4>] (SyS_ioctl+0x34/0x58)
[ 519.144649] [<800f43b4>] (SyS_ioctl) from [<80009000>] (ret_fast_syscall+0x0/0x28)
[ 519.152218] Exception stack(0x9f707fa8 to 0x9f707ff0)
[ 519.157275] 7fa0: 59790000 00000000 00000004 0000ab04 76f316ac 00000001
[ 519.165454] 7fc0: 59790000 00000000 00000004 00000036 00000001 00000000 00000000 7ef7ce04
[ 519.173633] 7fe0: 00023a9c 7ef7c984 000125c4 76ebcb7c
102080 bytes
# [ 519.219735] nbd0: p1 p2
[ 519.222468] nbd0: p1 size 5863680 extends beyond EOD, truncated
[ 519.237500] nbd0: p2 start 5761760 is beyond EOD, truncated
