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| author | Jens Axboe <axboe@kernel.dk> | 2018-11-09 15:58:40 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-11-10 08:16:12 -0700 |
| commit | de7b75d82f70c5469675b99ad632983c50b6f7e7 (patch) | |
| tree | ed79cfb552868a188101002ee9d862c95ad527e4 /drivers/block/floppy.c | |
| parent | dc5db21865507d0d9f706bd97c4a85315d60d0c5 (diff) | |
| download | lwn-de7b75d82f70c5469675b99ad632983c50b6f7e7.tar.gz lwn-de7b75d82f70c5469675b99ad632983c50b6f7e7.zip | |
floppy: fix race condition in __floppy_read_block_0()
LKP recently reported a hang at bootup in the floppy code:
[ 245.678853] INFO: task mount:580 blocked for more than 120 seconds.
[ 245.679906] Tainted: G T 4.19.0-rc6-00172-ga9f38e1 #1
[ 245.680959] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 245.682181] mount D 6372 580 1 0x00000004
[ 245.683023] Call Trace:
[ 245.683425] __schedule+0x2df/0x570
[ 245.683975] schedule+0x2d/0x80
[ 245.684476] schedule_timeout+0x19d/0x330
[ 245.685090] ? wait_for_common+0xa5/0x170
[ 245.685735] wait_for_common+0xac/0x170
[ 245.686339] ? do_sched_yield+0x90/0x90
[ 245.686935] wait_for_completion+0x12/0x20
[ 245.687571] __floppy_read_block_0+0xfb/0x150
[ 245.688244] ? floppy_resume+0x40/0x40
[ 245.688844] floppy_revalidate+0x20f/0x240
[ 245.689486] check_disk_change+0x43/0x60
[ 245.690087] floppy_open+0x1ea/0x360
[ 245.690653] __blkdev_get+0xb4/0x4d0
[ 245.691212] ? blkdev_get+0x1db/0x370
[ 245.691777] blkdev_get+0x1f3/0x370
[ 245.692351] ? path_put+0x15/0x20
[ 245.692871] ? lookup_bdev+0x4b/0x90
[ 245.693539] blkdev_get_by_path+0x3d/0x80
[ 245.694165] mount_bdev+0x2a/0x190
[ 245.694695] squashfs_mount+0x10/0x20
[ 245.695271] ? squashfs_alloc_inode+0x30/0x30
[ 245.695960] mount_fs+0xf/0x90
[ 245.696451] vfs_kern_mount+0x43/0x130
[ 245.697036] do_mount+0x187/0xc40
[ 245.697563] ? memdup_user+0x28/0x50
[ 245.698124] ksys_mount+0x60/0xc0
[ 245.698639] sys_mount+0x19/0x20
[ 245.699167] do_int80_syscall_32+0x61/0x130
[ 245.699813] entry_INT80_32+0xc7/0xc7
showing that we never complete that read request. The reason is that
the completion setup is racy - it initializes the completion event
AFTER submitting the IO, which means that the IO could complete
before/during the init. If it does, we are passing garbage to
complete() and we may sleep forever waiting for the event to
occur.
Fixes: 7b7b68bba5ef ("floppy: bail out in open() if drive is not responding to block0 read")
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block/floppy.c')
| -rw-r--r-- | drivers/block/floppy.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c index a8cfa011c284..fb23578e9a41 100644 --- a/drivers/block/floppy.c +++ b/drivers/block/floppy.c @@ -4148,10 +4148,11 @@ static int __floppy_read_block_0(struct block_device *bdev, int drive) bio.bi_end_io = floppy_rb0_cb; bio_set_op_attrs(&bio, REQ_OP_READ, 0); + init_completion(&cbdata.complete); + submit_bio(&bio); process_fd_request(); - init_completion(&cbdata.complete); wait_for_completion(&cbdata.complete); __free_page(page); |