quota: flush quota_release_work upon quota writeback

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: quota: flush quota_release_work upon quota writeback One of the paths quota writeback is called from is: freeze_super() sync_filesystem() ext4_sync_fs() dquot_writeback_dquots() Since we currently don't always flush the quota_release_work queue in this path, we can end up with the following race: 1. dquot are added to releasing_dquots list during regular operations. 2. FS Freeze starts, however, this does not flush the quota_release_work queue. 3. Freeze completes. 4. Kernel eventually tries to flush the workqueue while FS is frozen which hits a WARN_ON since transaction gets started during frozen state: ext4_journal_check_start+0x28/0x110 [ext4] (unreliable) __ext4_journal_start_sb+0x64/0x1c0 [ext4] ext4_release_dquot+0x90/0x1d0 [ext4] quota_release_workfn+0x43c/0x4d0 Which is the following line: WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE); Which ultimately results in generic/390 failing due to dmesg noise. This was detected on powerpc machine 15 cores. To avoid this, make sure to flush the workqueue during dquot_writeback_dquots() so we dont have any pending workitems after freeze.

References

• https://git.kernel.org/stable/c/a5abba5e0e586e258ded3e798fe5f69c66fec198
• https://git.kernel.org/stable/c/6f3821acd7c3143145999248087de5fb4b48cf26
• https://git.kernel.org/stable/c/ab6cfcf8ed2c7496f55d020b65b1d8cd55d9a2cb
• https://git.kernel.org/stable/c/3e6ff207cd5bd924ad94cd1a7c633bcdac0ba1cb
• https://git.kernel.org/stable/c/bcacb52a985f1b6d280f698a470b873dfe52728a
• https://git.kernel.org/stable/c/8ea87e34792258825d290f4dc5216276e91cb224
• https://git.kernel.org/stable/c/ac6f420291b3fee1113f21d612fa88b628afab5b