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d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pJvvFanCuFstEBJXi7mU85Wroh06uJ+VOOWdDKxnZ5I=; b=Biw5qKitXrT8+epI+dyARJWighBieLN4PHDDLLl+VASZngrzQRA2cXfAwnr7wBeCBU qb4u+VP8hnoaWJZUpzhgj8sG89JtBxMQHOzraDAuN8XEru9OyRqNehdASvO8AxWYEqBY AOTs4NKw4LNNykAlvfO4r5t9hBOxuphSufcfTcCLsrVgylLgiNjQt0KziWqE8eTVJWXY jmeykhUYXBUZZ66dnUhw7DHQTZYhl3cQntglZSKBZdX16VCtnBG34vF+KPLz+4Xzt1p7 Qw9HtxcnY8v8U8yf+XA+G9JJ+P0fRKopwBAMa+0cSP589bvpBRhR+wYOgdFf94uCIXS9 MtMA== X-Gm-Message-State: AOAM533IsSG4gXxMdfBcxJzGme/Lz8T+kWGlnZUfPIVkcp3HcTFXinvO nUyoXlKdVQvhbR8r6IuPuOd3vi9Zy/OM/9yCIoxBcg== X-Google-Smtp-Source: ABdhPJxHo1cWxV3tneBHQX3C0hiqTH0ycLZDOrND1B5gNYL3V/dxlD7pzeFkL9SnWn2MB4KQOtaBb/4waIkuaUlQt+o= X-Received: by 2002:a05:6870:9619:b0:d9:a25e:ed55 with SMTP id d25-20020a056870961900b000d9a25eed55mr1899508oaq.163.1648111826186; Thu, 24 Mar 2022 01:50:26 -0700 (PDT) MIME-Version: 1.0 References: <000000000000cabcb505dae9e577@google.com> In-Reply-To: From: Dmitry Vyukov Date: Thu, 24 Mar 2022 09:50:14 +0100 Message-ID: Subject: Re: [syzbot] general protection fault in list_lru_add To: Muchun Song Cc: Linus Torvalds , syzbot , Andrew Morton , Linux Kernel Mailing List , Linux-MM , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 4803540034 X-Stat-Signature: r5okzemhhegkipoubud3z9hjmjobs6za Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=p1BZOeWm; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf01.hostedemail.com: domain of dvyukov@google.com designates 209.85.160.53 as permitted sender) smtp.mailfrom=dvyukov@google.com X-Rspam-User: X-HE-Tag: 1648111827-130943 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 24 Mar 2022 at 09:44, Muchun Song wrote: > > On Thu, Mar 24, 2022 at 11:05 AM Linus Torvalds > wrote: > > > > On Wed, Mar 23, 2022 at 7:19 PM Muchun Song wrote: > > > > > > After this commit, the rules of dentry allocations changed. > > > The dentry should be allocated by kmem_cache_alloc_lru() > > > > Yeah, I looked at that, but I can't find any way there could be other > > allocations - not only are there strict rules how to initialize > > everything, but the dentries are free'd using > > > > kmem_cache_free(dentry_cache, dentry); > > > > and as a result if they were allocated any other way I would expect > > things would go south very quickly. > > > > The only other thing I could come up with is some breakage in the > > superblock lifetime so that &dentry->d_sb->s_dentry_lru would have > > problems, but again, this is *such* core code and not some unusual > > path, that I would be very very surprised if it wouldn't have > > triggered other issues long long ago. > > > > That's why I'd be more inclined to worry about the list_lru code being > > somehow broken. > > > > I also have the same concern. I have been trying for a few hours to > reproduce this issue, but it didn't oops on my test machine. And I'll > continue reproducing this. syzbot triggered it 222 times in a day, so it's most likely real: https://syzkaller.appspot.com/bug?extid=f8c45ccc7d5d45fc5965 There are 2 reproducers, but they look completely different. May be a race. You may also try to use syzbot's patch testing feature to get some additional debug info.