mtd: block: prevent reclaim I/O during request processing

The blktrans request callbacks run under dev->lock and may allocate
memory with GFP_KERNEL. For example, mtdblock_writesect() uses vmalloc()
to allocate its eraseblock cache. Direct reclaim can then recurse into
block I/O and deadlock on resources held by the request being processed.
syzbot reports a circular locking dependency involving the device mutex
and fs_reclaim.

Commit d5ba1c8ffd0b ("mtd: don't use PF_MEMALLOC") removed PF_MEMALLOC
from the MTD request thread. That flag had prevented direct reclaim,
so its removal made allocations during request processing eligible for
reclaim without excluding I/O.

Wrap request processing in mtd_queue_rq() in a NOIO scope. This covers
both the request and background callbacks, including allocations made
by lower MTD drivers, and prevents reclaim from initiating filesystem
or block I/O.

Fixes: d5ba1c8ffd0b ("mtd: don't use PF_MEMALLOC")
Assisted-by: Codex:gpt-6-astra
Reported-by: syzbot+e08e0a15269eefa87790@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=e08e0a15269eefa87790
Signed-off-by: Qingfang Deng <qingfang.deng@linux.dev>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

0 files changed, 0 insertions, 0 deletions