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Sat, 21 Mar 2026 07:17:08 -0700 (PDT) Message-ID: Date: Sat, 21 Mar 2026 08:17:06 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH next] block: mempool alloc fail due to insufficient memory To: Edward Adam Davis , syzbot+09ddb593eea76a158f42@syzkaller.appspotmail.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com References: <69bdcdcd.050a0220.3bf4de.002f.GAE@google.com> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/21/26 2:36 AM, Edward Adam Davis wrote: > Add a failure check for mempool_alloc() in the slowpath. > > [1] > KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] > Workqueue: writeback wb_workfn (flush-8:0) > RIP: 0010:bio_init block/bio.c:214 [inline] > RIP: 0010:bio_init_inline include/linux/bio.h:435 [inline] > RIP: 0010:bio_alloc_bioset+0x664/0xc10 block/bio.c:593 > Call Trace: > bio_alloc include/linux/bio.h:373 [inline] > submit_bh_wbc+0x22d/0x650 fs/buffer.c:2816 > > Fixes: b520c4eef83d ("block: split bio_alloc_bioset more clearly into a fast and slowpath") > Reported-by: syzbot+09ddb593eea76a158f42@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=09ddb593eea76a158f42 > Signed-off-by: Edward Adam Davis > --- > block/bio.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/block/bio.c b/block/bio.c > index 5057047194c4..0a870979bd41 100644 > --- a/block/bio.c > +++ b/block/bio.c > @@ -582,6 +582,9 @@ struct bio *bio_alloc_bioset(struct block_device *bdev, unsigned short nr_vecs, > opf &= ~REQ_ALLOC_CACHE; > > p = mempool_alloc(&bs->bio_pool, gfp); > + if (unlikely(!p)) > + return NULL; > + Doesn't look right at all. You dropped the backtrace, which shows this is off __block_write_full_folio() -> submit_bh_wbc() which allocates a bio from the mempool with GFP_NOIO. That should allow blocking, and hence mempool_alloc() should NEVER return NULL for that case. If it does, it's broken, and your change is just papering around that issue. -- Jens Axboe