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[2003:dc:6f19:d800:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ab786aa2c60sm812424766b.102.2025.02.10.11.11.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Feb 2025 11:11:22 -0800 (PST) From: Max Kellermann To: dhowells@redhat.com, netfs@lists.linux.dev, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org Cc: Max Kellermann Subject: [PATCH] fs/netfs/read_collect: add to next->prev_donated Date: Mon, 10 Feb 2025 20:11:18 +0100 Message-ID: <20250210191118.3444416-1-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.2 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" If multiple subrequests donate data to the same "next" request (depending on the subrequest completion order), each of them would overwrite the `prev_donated` field, causing data corruption and a BUG() crash ("Can't donate prior to front"). Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading") Closes: https://lore.kernel.org/netfs/CAKPOu+_4mUwYgQtRTbXCmi+-k3PGvLysnPad= kmHOyB7Gz0iSMA@mail.gmail.com/ Signed-off-by: Max Kellermann --- David, this seems to fix the bug for me. Please also check if we need a "donation_changed" check. --- fs/netfs/read_collect.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c index 0d95cdbe5611..681b630b4f06 100644 --- a/fs/netfs/read_collect.c +++ b/fs/netfs/read_collect.c @@ -284,7 +284,7 @@ static bool netfs_consume_read_data(struct netfs_io_sub= request *subreq, bool was netfs_trace_donate_to_deferred_next); } else { next =3D list_next_entry(subreq, rreq_link); - WRITE_ONCE(next->prev_donated, excess); + WRITE_ONCE(next->prev_donated, next->prev_donated + excess); trace_netfs_donate(rreq, subreq, next, excess, netfs_trace_donate_to_next); } --=20 2.47.2