ext4: fast commit: avoid self-deadlock in inode snapshotting

ext4_fc_snapshot_inodes() used igrab()/iput() to pin inodes while building
commit-time snapshots. With ext4_fc_del() waiting for
EXT4_STATE_FC_COMMITTING, iput() can trigger
ext4_clear_inode()->ext4_fc_del() in the commit thread and deadlock waiting
for the fast commit to finish.

ext4_fc_del() also has to re-check EXT4_STATE_FC_COMMITTING after
waiting on EXT4_STATE_FC_FLUSHING_DATA. The commit thread clears
FLUSHING_DATA before it sets COMMITTING, so a waiter woken from the
flush wait must not delete the inode based on an old COMMITTING
check.

Avoid taking extra references. Collect inode pointers under s_fc_lock and
rely on EXT4_STATE_FC_COMMITTING to pin inodes until ext4_fc_cleanup()
clears the bit.

Also set EXT4_STATE_FC_COMMITTING for create-only inodes referenced
from the dentry update queue, and wake up waiters when ext4_fc_cleanup()
clears the bit.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Link: https://patch.msgid.link/20260515091829.194810-5-me@linux.beauty
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

0 files changed, 0 insertions, 0 deletions