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31464ab01f
We got a NULL pointer dereference issue below while running generic/475 I/O failure pressure test. BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] PREEMPT SMP PTI CPU: 1 PID: 15600 Comm: fsstress Not tainted 6.4.0-rc5-xfstests-00055-gd3ab1bca26b4 #190 RIP: 0010:jbd2_journal_set_features+0x13d/0x430 ... Call Trace: <TASK> ? __die+0x23/0x60 ? page_fault_oops+0xa4/0x170 ? exc_page_fault+0x67/0x170 ? asm_exc_page_fault+0x26/0x30 ? jbd2_journal_set_features+0x13d/0x430 jbd2_journal_revoke+0x47/0x1e0 __ext4_forget+0xc3/0x1b0 ext4_free_blocks+0x214/0x2f0 ext4_free_branches+0xeb/0x270 ext4_ind_truncate+0x2bf/0x320 ext4_truncate+0x1e4/0x490 ext4_handle_inode_extension+0x1bd/0x2a0 ? iomap_dio_complete+0xaf/0x1d0 The root cause is the journal super block had been failed to write out due to I/O fault injection, it's uptodate bit was cleared by end_buffer_write_sync() and didn't reset yet in jbd2_write_superblock(). And it raced by journal_get_superblock()->bh_read(), unfortunately, the read IO is also failed, so the error handling in journal_fail_superblock() unexpectedly clear the journal->j_sb_buffer, finally lead to above NULL pointer dereference issue. If the journal super block had been read and verified, there is no need to call bh_read() read it again even if it has been failed to written out. So the fix could be simply move buffer_verified(bh) in front of bh_read(). Also remove a stale comment left in jbd2_journal_check_used_features(). Fixes: 51bacdba23d8 ("jbd2: factor out journal initialization from journal_get_superblock()") Reported-by: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Zhang Yi <yi.zhang@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20230616015547.3155195-1-yi.zhang@huaweicloud.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.