On Tue 15-09-20 22:57:35, zhangyi (F) wrote: > Hi, Jan > > On 2020/9/15 21:07, Jan Kara wrote: > > On Mon 14-09-20 19:24:20, zhangyi (F) wrote: > >> 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 clear buffer's verified bit if we read it from disk again. > >> > >> Signed-off-by: zhangyi (F) <yi.zhang@xxxxxxxxxx> > > > > Good spotting! When looking at the patch I was just wondering that it's > > rather easy to miss clearing of buffer_verified() bit in some place where > > we read metadata block from disk. So I was wondering that maybe it would be > > Indeed, I clear the buffer_verified() bit in some common helpers of ext4, > such as ext4_bread() and ext4_sb_bread(), so we may not miss clear it > where we invoke these helpers, but it is rather easy to miss in the > others places where submit read bio directly. How about add some common > helpers for them too ? I was thinking about this for some time and yes, I agree this is probably the best way forward. I've looked at places where we submit reads and probably some helper like below should work: void ext4_read_bh(struct buffer_head *bh, int op_flags, void (*end_io)(struct buffer_head *bh, int uptodate)) which would do the final ext4_buffer_uptodate() check, set end_io (fill in end_buffer_read_sync if NULL), clear verified bit, get bh ref, and do submit_bh(). And use this in all the places reading metadata buffers instead of various different helpers. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
