nilfs2: fix potential kernel bug due to lack of writeback flag waiting

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix potential kernel bug due to lack of writeback flag waiting Destructive writes to a block device on which nilfs2 is mounted can cause a kernel bug in the folio/page writeback start routine or writeback end routine (__folio_start_writeback in the log below): kernel BUG at mm/page-writeback.c:3070! Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI ... RIP: 0010:__folio_start_writeback+0xbaa/0x10e0 Code: 25 ff 0f 00 00 0f 84 18 01 00 00 e8 40 ca c6 ff e9 17 f6 ff ff e8 36 ca c6 ff 4c 89 f7 48 c7 c6 80 c0 12 84 e8 e7 b3 0f 00 90 <0f> 0b e8 1f ca c6 ff 4c 89 f7 48 c7 c6 a0 c6 12 84 e8 d0 b3 0f 00 ... Call Trace: <TASK> nilfs_segctor_do_construct+0x4654/0x69d0 [nilfs2] nilfs_segctor_construct+0x181/0x6b0 [nilfs2] nilfs_segctor_thread+0x548/0x11c0 [nilfs2] kthread+0x2f0/0x390 ret_from_fork+0x4b/0x80 ret_from_fork_asm+0x1a/0x30 </TASK> This is because when the log writer starts a writeback for segment summary blocks or a super root block that use the backing device's page cache, it does not wait for the ongoing folio/page writeback, resulting in an inconsistent writeback state. Fix this issue by waiting for ongoing writebacks when putting folios/pages on the backing device into writeback state.

References

• https://git.kernel.org/stable/c/95f6f81e50d858a7c9aa7c795ec14a0ac3819118
• https://git.kernel.org/stable/c/a75b8f493dfc48aa38c518430bd9e03b53bffebe
• https://git.kernel.org/stable/c/0ecfe3a92869a59668d27228dabbd7965e83567f
• https://git.kernel.org/stable/c/33900d7eae616647e179eee1c66ebe654ee39627
• https://git.kernel.org/stable/c/271dcd977ccda8c7a26e360425ae7b4db7d2ecc0
• https://git.kernel.org/stable/c/614d397be0cf43412b3f94a0f6460eddced8ce92
• https://git.kernel.org/stable/c/1f3bff69f1214fe03a02bc650d5bbfaa6e65ae7d
• https://git.kernel.org/stable/c/a4ca369ca221bb7e06c725792ac107f0e48e82e7