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be1ee45d51
In the cache writing process, if it is an atomic file, increase the page
count of F2FS_WB_CP_DATA, otherwise increase the page count of
F2FS_WB_DATA.
When you step into the hook branch due to insufficient memory in
f2fs_write_begin, f2fs_drop_inmem_pages_all will be called to traverse
all atomic inodes and clear the FI_ATOMIC_FILE mark of all atomic files.
In f2fs_drop_inmem_pages，first acquire the inmem_lock , revoke all the
inmem_pages, and then clear the FI_ATOMIC_FILE mark. Before this mark is
cleared, other threads may hold inmem_lock to add inmem_pages to the inode
that has just been emptied inmem_pages, and increase the page count of
F2FS_WB_CP_DATA.
When the IO returns, it is found that the FI_ATOMIC_FILE flag is cleared
by f2fs_drop_inmem_pages_all, and f2fs_is_atomic_file returns false,which
causes the page count of F2FS_WB_DATA to be decremented. The page count of
F2FS_WB_CP_DATA cannot be cleared. Finally, hungtask is triggered in
f2fs_wait_on_all_pages because get_pages will never return zero.
process A: process B:
f2fs_drop_inmem_pages_all
->f2fs_drop_inmem_pages of inode#1
->mutex_lock(&fi->inmem_lock)
->__revoke_inmem_pages of inode#1 f2fs_ioc_commit_atomic_write
->mutex_unlock(&fi->inmem_lock) ->f2fs_commit_inmem_pages of inode#1
->mutex_lock(&fi->inmem_lock)
->__f2fs_commit_inmem_pages
->f2fs_do_write_data_page
->f2fs_outplace_write_data
->do_write_page
->f2fs_submit_page_write
->inc_page_count(sbi, F2FS_WB_CP_DATA )
->mutex_unlock(&fi->inmem_lock)
->spin_lock(&sbi->inode_lock[ATOMIC_FILE]);
->clear_inode_flag(inode, FI_ATOMIC_FILE)
->spin_unlock(&sbi->inode_lock[ATOMIC_FILE])
f2fs_write_end_io
->dec_page_count(sbi, F2FS_WB_DATA );
We can fix the problem by putting the action of clearing the FI_ATOMIC_FILE
mark into the inmem_lock lock. This operation can ensure that no one will
submit the inmem pages before the FI_ATOMIC_FILE mark is cleared, so that
there will be no atomic writes waiting for writeback.
Fixes:
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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.