4.4-stable review patch. If anyone has any objections, please let me know.
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From: Maurizio Lombardi mlombard@redhat.com
[ Upstream commit 2bbea6e117357d17842114c65e9a9cf2d13ae8a3 ]
when mounting an ISO filesystem sometimes (very rarely) the system hangs because of a race condition between two tasks.
PID: 6766 TASK: ffff88007b2a6dd0 CPU: 0 COMMAND: "mount" #0 [ffff880078447ae0] __schedule at ffffffff8168d605 #1 [ffff880078447b48] schedule_preempt_disabled at ffffffff8168ed49 #2 [ffff880078447b58] __mutex_lock_slowpath at ffffffff8168c995 #3 [ffff880078447bb8] mutex_lock at ffffffff8168bdef #4 [ffff880078447bd0] sr_block_ioctl at ffffffffa00b6818 [sr_mod] #5 [ffff880078447c10] blkdev_ioctl at ffffffff812fea50 #6 [ffff880078447c70] ioctl_by_bdev at ffffffff8123a8b3 #7 [ffff880078447c90] isofs_fill_super at ffffffffa04fb1e1 [isofs] #8 [ffff880078447da8] mount_bdev at ffffffff81202570 #9 [ffff880078447e18] isofs_mount at ffffffffa04f9828 [isofs] #10 [ffff880078447e28] mount_fs at ffffffff81202d09 #11 [ffff880078447e70] vfs_kern_mount at ffffffff8121ea8f #12 [ffff880078447ea8] do_mount at ffffffff81220fee #13 [ffff880078447f28] sys_mount at ffffffff812218d6 #14 [ffff880078447f80] system_call_fastpath at ffffffff81698c49 RIP: 00007fd9ea914e9a RSP: 00007ffd5d9bf648 RFLAGS: 00010246 RAX: 00000000000000a5 RBX: ffffffff81698c49 RCX: 0000000000000010 RDX: 00007fd9ec2bc210 RSI: 00007fd9ec2bc290 RDI: 00007fd9ec2bcf30 RBP: 0000000000000000 R8: 0000000000000000 R9: 0000000000000010 R10: 00000000c0ed0001 R11: 0000000000000206 R12: 00007fd9ec2bc040 R13: 00007fd9eb6b2380 R14: 00007fd9ec2bc210 R15: 00007fd9ec2bcf30 ORIG_RAX: 00000000000000a5 CS: 0033 SS: 002b
This task was trying to mount the cdrom. It allocated and configured a super_block struct and owned the write-lock for the super_block->s_umount rwsem. While exclusively owning the s_umount lock, it called sr_block_ioctl and waited to acquire the global sr_mutex lock.
PID: 6785 TASK: ffff880078720fb0 CPU: 0 COMMAND: "systemd-udevd" #0 [ffff880078417898] __schedule at ffffffff8168d605 #1 [ffff880078417900] schedule at ffffffff8168dc59 #2 [ffff880078417910] rwsem_down_read_failed at ffffffff8168f605 #3 [ffff880078417980] call_rwsem_down_read_failed at ffffffff81328838 #4 [ffff8800784179d0] down_read at ffffffff8168cde0 #5 [ffff8800784179e8] get_super at ffffffff81201cc7 #6 [ffff880078417a10] __invalidate_device at ffffffff8123a8de #7 [ffff880078417a40] flush_disk at ffffffff8123a94b #8 [ffff880078417a88] check_disk_change at ffffffff8123ab50 #9 [ffff880078417ab0] cdrom_open at ffffffffa00a29e1 [cdrom] #10 [ffff880078417b68] sr_block_open at ffffffffa00b6f9b [sr_mod] #11 [ffff880078417b98] __blkdev_get at ffffffff8123ba86 #12 [ffff880078417bf0] blkdev_get at ffffffff8123bd65 #13 [ffff880078417c78] blkdev_open at ffffffff8123bf9b #14 [ffff880078417c90] do_dentry_open at ffffffff811fc7f7 #15 [ffff880078417cd8] vfs_open at ffffffff811fc9cf #16 [ffff880078417d00] do_last at ffffffff8120d53d #17 [ffff880078417db0] path_openat at ffffffff8120e6b2 #18 [ffff880078417e48] do_filp_open at ffffffff8121082b #19 [ffff880078417f18] do_sys_open at ffffffff811fdd33 #20 [ffff880078417f70] sys_open at ffffffff811fde4e #21 [ffff880078417f80] system_call_fastpath at ffffffff81698c49 RIP: 00007f29438b0c20 RSP: 00007ffc76624b78 RFLAGS: 00010246 RAX: 0000000000000002 RBX: ffffffff81698c49 RCX: 0000000000000000 RDX: 00007f2944a5fa70 RSI: 00000000000a0800 RDI: 00007f2944a5fa70 RBP: 00007f2944a5f540 R8: 0000000000000000 R9: 0000000000000020 R10: 00007f2943614c40 R11: 0000000000000246 R12: ffffffff811fde4e R13: ffff880078417f78 R14: 000000000000000c R15: 00007f2944a4b010 ORIG_RAX: 0000000000000002 CS: 0033 SS: 002b
This task tried to open the cdrom device, the sr_block_open function acquired the global sr_mutex lock. The call to check_disk_change() then saw an event flag indicating a possible media change and tried to flush any cached data for the device. As part of the flush, it tried to acquire the super_block->s_umount lock associated with the cdrom device. This was the same super_block as created and locked by the previous task.
The first task acquires the s_umount lock and then the sr_mutex_lock; the second task acquires the sr_mutex_lock and then the s_umount lock.
This patch fixes the issue by moving check_disk_change() out of cdrom_open() and let the caller take care of it.
Signed-off-by: Maurizio Lombardi mlombard@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/block/paride/pcd.c | 2 ++ drivers/cdrom/cdrom.c | 3 --- drivers/cdrom/gdrom.c | 3 +++ drivers/ide/ide-cd.c | 2 ++ drivers/scsi/sr.c | 2 ++ 5 files changed, 9 insertions(+), 3 deletions(-)
--- a/drivers/block/paride/pcd.c +++ b/drivers/block/paride/pcd.c @@ -230,6 +230,8 @@ static int pcd_block_open(struct block_d struct pcd_unit *cd = bdev->bd_disk->private_data; int ret;
+ check_disk_change(bdev); + mutex_lock(&pcd_mutex); ret = cdrom_open(&cd->info, bdev, mode); mutex_unlock(&pcd_mutex); --- a/drivers/cdrom/cdrom.c +++ b/drivers/cdrom/cdrom.c @@ -1154,9 +1154,6 @@ int cdrom_open(struct cdrom_device_info
cd_dbg(CD_OPEN, "entering cdrom_open\n");
- /* open is event synchronization point, check events first */ - check_disk_change(bdev); - /* if this was a O_NONBLOCK open and we should honor the flags, * do a quick open without drive/disc integrity checks. */ cdi->use_count++; --- a/drivers/cdrom/gdrom.c +++ b/drivers/cdrom/gdrom.c @@ -497,6 +497,9 @@ static struct cdrom_device_ops gdrom_ops static int gdrom_bdops_open(struct block_device *bdev, fmode_t mode) { int ret; + + check_disk_change(bdev); + mutex_lock(&gdrom_mutex); ret = cdrom_open(gd.cd_info, bdev, mode); mutex_unlock(&gdrom_mutex); --- a/drivers/ide/ide-cd.c +++ b/drivers/ide/ide-cd.c @@ -1593,6 +1593,8 @@ static int idecd_open(struct block_devic struct cdrom_info *info; int rc = -ENXIO;
+ check_disk_change(bdev); + mutex_lock(&ide_cd_mutex); info = ide_cd_get(bdev->bd_disk); if (!info) --- a/drivers/scsi/sr.c +++ b/drivers/scsi/sr.c @@ -522,6 +522,8 @@ static int sr_block_open(struct block_de struct scsi_cd *cd; int ret = -ENXIO;
+ check_disk_change(bdev); + mutex_lock(&sr_mutex); cd = scsi_cd_get(bdev->bd_disk); if (cd) {