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The metadata buffer is no longer trusted after we read it from disk again because it is not uptodate for some reasons (e.g. failed to write back). Otherwise we may get below memory corruption problem in ext4_ext_split()->memset() if we read stale data from the newly allocated extent block on disk which has been failed to async write out but miss verify again since the verified bit has already been set on the buffer. [ 29.774674] BUG: unable to handle kernel paging request at ffff88841949d000 ... [ 29.783317] Oops: 0002 [#2] SMP [ 29.784219] R10: 00000000000f4240 R11: 0000000000002e28 R12: ffff88842fa1c800 [ 29.784627] CPU: 1 PID: 126 Comm: kworker/u4:3 Tainted: G D W [ 29.785546] R13: ffffffff9cddcc20 R14: ffffffff9cddd420 R15: ffff88842fa1c2f8 [ 29.786679] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),BIOS ?-20190727_0738364 [ 29.787588] FS: 0000000000000000(0000) GS:ffff88842fa00000(0000) knlGS:0000000000000000 [ 29.789288] Workqueue: writeback wb_workfn [ 29.790319] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 29.790321] (flush-8:0) [ 29.790844] CR2: 0000000000000008 CR3: 00000004234f2000 CR4: 00000000000006f0 [ 29.791924] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 29.792839] RIP: 0010:__memset+0x24/0x30 [ 29.793739] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 29.794256] Code: 90 90 90 90 90 90 0f 1f 44 00 00 49 89 f9 48 89 d1 83 e2 07 48 c1 e9 033 [ 29.795161] Kernel panic - not syncing: Fatal exception in interrupt ... [ 29.808149] Call Trace: [ 29.808475] ext4_ext_insert_extent+0x102e/0x1be0 [ 29.809085] ext4_ext_map_blocks+0xa89/0x1bb0 [ 29.809652] ext4_map_blocks+0x290/0x8a0 [ 29.809085] ext4_ext_map_blocks+0xa89/0x1bb0 [ 29.809652] ext4_map_blocks+0x290/0x8a0 [ 29.810161] ext4_writepages+0xc85/0x17c0 ... Fix this by clearing buffer's verified bit if we read meta block from disk again. Signed-off-by: zhangyi (F) <yi.zhang@huawei.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200924073337.861472-2-yi.zhang@huawei.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.