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da0386c1c7
The conversion to folios switched __free_page() to __folio_put() in the
error path in btrfs_do_encoded_write().
However, this gets the page refcounting wrong. If we do hit that error
path (I reproduced by modifying btrfs_do_encoded_write to pretend to
always fail in a way that jumps to out_folios and running the fstests
case btrfs/281), then we always hit the following BUG freeing the folio:
BUG: Bad page state in process btrfs pfn:40ab0b
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x61be5 pfn:0x40ab0b
flags: 0x5ffff0000000000(node=0|zone=2|lastcpupid=0x1ffff)
raw: 05ffff0000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000061be5 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: nonzero _refcount
Call Trace:
<TASK>
dump_stack_lvl+0x3d/0xe0
bad_page+0xea/0xf0
free_unref_page+0x8e1/0x900
? __mem_cgroup_uncharge+0x69/0x90
__folio_put+0xe6/0x190
btrfs_do_encoded_write+0x445/0x780
? current_time+0x25/0xd0
btrfs_do_write_iter+0x2cc/0x4b0
btrfs_ioctl_encoded_write+0x2b6/0x340
It turns out __free_page() decreases the page reference count while
__folio_put() does not. Switch __folio_put() to folio_put() which
decreases the folio reference count first.
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 reStructuredText 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.