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Tue, 28 Apr 2026 04:53:48 -0700 (PDT) From: Abd-Alrhman Masalkhi To: Yu Kuai , song@kernel.org, paul.e.luse@linux.intel.com, xni@redhat.com, yukuai@fnnas.com Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] md/raid1: fix len reuse across rdevs in choose_first_rdev() In-Reply-To: <5c71cb6b-d860-4bcb-a900-a27544be7a17@fnnas.com> References: <20260426093506.14316-1-abd.masalkhi@gmail.com> <5c71cb6b-d860-4bcb-a900-a27544be7a17@fnnas.com> Date: Tue, 28 Apr 2026 13:53:45 +0200 Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Kaui, On Tue, Apr 28, 2026 at 16:23 +0800, Yu Kuai wrote: > Hi, > > =E5=9C=A8 2026/4/26 17:35, Abd-Alrhman Masalkhi =E5=86=99=E9=81=93: >> choose_first_rdev() initializes the variable len before iterating over >> all rdevs, but passes it by reference to raid1_check_read_range(), which >> it might update *len and return 0 depending on the layout of the bad >> block region. As a result, 'len' can be modified during the first >> iteration and reused for subsequent rdevs, causing later devices to be >> evaluated with an incorrect length value. >> >> Fixes: 31a73331752d3 ("md/raid1: factor out read_first_rdev() from read_= balance()") >> Signed-off-by: Abd-Alrhman Masalkhi >> --- >> drivers/md/raid1.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c >> index b549be9174bb..5f5dbf79c903 100644 >> --- a/drivers/md/raid1.c >> +++ b/drivers/md/raid1.c >> @@ -591,12 +591,12 @@ static int choose_first_rdev(struct r1conf *conf, = struct r1bio *r1_bio, >> int *max_sectors) >> { >> sector_t this_sector =3D r1_bio->sector; >> - int len =3D r1_bio->sectors; >> int disk; >>=20=20=20 >> for (disk =3D 0 ; disk < conf->raid_disks * 2 ; disk++) { >> struct md_rdev *rdev; >> int read_len; >> + int len =3D r1_bio->sectors; >>=20=20=20 >> if (r1_bio->bios[disk] =3D=3D IO_BLOCKED) >> continue; > > This patch is wrong, choose_first_rdev() is used when raid1_should_read_f= irst() is true, > meaning the read overlaps an unsynced/resyncing area. Reset len can cause= the problem that > reading the same area can return different data. > Thank you for the detailed explanation. After carefully re-reading the code and your feedback, I understand why the patch is wrong. > --=20 > Thansk, > Kuai --=20 Best Regards, Abd-Alrhman