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2dfb1e43f5
[BUG]
When the anonymous block device pool is exhausted, subvolume/snapshot
creation fails with EMFILE (Too many files open). This has been reported
by a user. The allocation happens in the second phase during transaction
commit where it's only way out is to abort the transaction
BTRFS: Transaction aborted (error -24)
WARNING: CPU: 17 PID: 17041 at fs/btrfs/transaction.c:1576 create_pending_snapshot+0xbc4/0xd10 [btrfs]
RIP: 0010:create_pending_snapshot+0xbc4/0xd10 [btrfs]
Call Trace:
create_pending_snapshots+0x82/0xa0 [btrfs]
btrfs_commit_transaction+0x275/0x8c0 [btrfs]
btrfs_mksubvol+0x4b9/0x500 [btrfs]
btrfs_ioctl_snap_create_transid+0x174/0x180 [btrfs]
btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs]
btrfs_ioctl+0x11a4/0x2da0 [btrfs]
do_vfs_ioctl+0xa9/0x640
ksys_ioctl+0x67/0x90
__x64_sys_ioctl+0x1a/0x20
do_syscall_64+0x5a/0x110
entry_SYSCALL_64_after_hwframe+0x44/0xa9
---[ end trace 33f2f83f3d5250e9 ]---
BTRFS: error (device sda1) in create_pending_snapshot:1576: errno=-24 unknown
BTRFS info (device sda1): forced readonly
BTRFS warning (device sda1): Skipping commit of aborted transaction.
BTRFS: error (device sda1) in cleanup_transaction:1831: errno=-24 unknown
[CAUSE]
When the global anonymous block device pool is exhausted, the following
call chain will fail, and lead to transaction abort:
btrfs_ioctl_snap_create_v2()
|- btrfs_ioctl_snap_create_transid()
|- btrfs_mksubvol()
|- btrfs_commit_transaction()
|- create_pending_snapshot()
|- btrfs_get_fs_root()
|- btrfs_init_fs_root()
|- get_anon_bdev()
[FIX]
Although we can't enlarge the anonymous block device pool, at least we
can preallocate anon_dev for subvolume/snapshot in the first phase,
outside of transaction context and exactly at the moment the user calls
the creation ioctl.
Reported-by: Greed Rong <greedrong@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CA+UqX+NTrZ6boGnWHhSeZmEY5J76CTqmYjO2S+=tHJX7nb9DPw@mail.gmail.com/
CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
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Linux kernel
============
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