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Mon, 06 Oct 2025 05:48:54 -0700 (PDT) Message-ID: Date: Mon, 6 Oct 2025 06:48:52 -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 v2] Revert "sunvdc: Do not spin in an infinite loop when vio_ldc_send() returns EAGAIN" To: John Paul Adrian Glaubitz , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Andreas Larsson , Anthony Yznaga , Sam James , "David S . Miller" , Michael Karcher , sparclinux@vger.kernel.org References: <20251006100226.4246-2-glaubitz@physik.fu-berlin.de> Content-Language: en-US From: Jens Axboe In-Reply-To: <20251006100226.4246-2-glaubitz@physik.fu-berlin.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/6/25 4:02 AM, John Paul Adrian Glaubitz wrote: > In a11f6ca9aef9 ("sunvdc: Do not spin in an infinite loop when vio_ldc_send() > returns EAGAIN"), a maximum retry count was added to __vdc_tx_trigger(). > > After this change, several users reported disk I/O errors when running Linux > inside a logical domain on Solaris 11.4: > > [19095.192532] sunvdc: vdc_tx_trigger() failure, err=-11 > [19095.192605] I/O error, dev vdiskc, sector 368208928 op 0x1:(WRITE) flags 0x1000 phys_seg 2 prio class 2 > [19095.205681] XFS (vdiskc1): metadata I/O error in "xfs_buf_ioend+0x28c/0x600 [xfs]" at daddr 0x15f26420 len 32 error 5 > [19432.043471] sunvdc: vdc_tx_trigger() failure, err=-11 > [19432.043529] I/O error, dev vdiskc, sector 3732568 op 0x1:(WRITE) flags 0x1000 phys_seg 1 prio class 2 > [19432.058821] sunvdc: vdc_tx_trigger() failure, err=-11 > [19432.058843] I/O error, dev vdiskc, sector 3736256 op 0x1:(WRITE) flags 0x1000 phys_seg 4 prio class 2 > [19432.074109] sunvdc: vdc_tx_trigger() failure, err=-11 > [19432.074128] I/O error, dev vdiskc, sector 3736512 op 0x1:(WRITE) flags 0x1000 phys_seg 4 prio class 2 > [19432.089425] sunvdc: vdc_tx_trigger() failure, err=-11 > [19432.089443] I/O error, dev vdiskc, sector 3737024 op 0x1:(WRITE) flags 0x1000 phys_seg 1 prio class 2 > [19432.100964] XFS (vdiskc1): metadata I/O error in "xfs_buf_ioend+0x28c/0x600 [xfs]" at daddr 0x38ec58 len 8 error 5 > > Since this change seems to have only been justified by reading the code which > becomes evident by the reference to adddc32d6fde ("sunvnet: Do not spin in an > infinite loop when vio_ldc_send() returns EAGAIN") in the commit message, it > can be safely assumed that the change was neither properly tested nor motivated > by any actual bug reports. > > Thus, let's revert this change to address the disk I/O errors above. > > Signed-off-by: John Paul Adrian Glaubitz > --- > Changes since v1: > - Rephrase commit message > --- > drivers/block/sunvdc.c | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c > index 282f81616a78..f56023c2b033 100644 > --- a/drivers/block/sunvdc.c > +++ b/drivers/block/sunvdc.c > @@ -45,8 +45,6 @@ MODULE_VERSION(DRV_MODULE_VERSION); > #define WAITING_FOR_GEN_CMD 0x04 > #define WAITING_FOR_ANY -1 > > -#define VDC_MAX_RETRIES 10 > - > static struct workqueue_struct *sunvdc_wq; > > struct vdc_req_entry { > @@ -437,7 +435,6 @@ static int __vdc_tx_trigger(struct vdc_port *port) > .end_idx = dr->prod, > }; > int err, delay; > - int retries = 0; > > hdr.seq = dr->snd_nxt; > delay = 1; > @@ -450,8 +447,6 @@ static int __vdc_tx_trigger(struct vdc_port *port) > udelay(delay); > if ((delay <<= 1) > 128) > delay = 128; > - if (retries++ > VDC_MAX_RETRIES) > - break; > } while (err == -EAGAIN); > > if (err == -ENOTCONN) When you apply this patch and things work, how many times does it generally spin where it would've failed before? It's a bit unnerving to have a never ending spin loop for this, with udelay spinning in between as well. Looking at vio_ldc_send() as well, that spins for potentially 1000 loops of 1usec each, which would be 1ms. With the current limit of 10 retries, the driver would end up doing udelays of: 1 2 4 8 16 32 64 128 128 128 which is 511 usec on top, for 10.5ms in total spinning time before giving up. That is kind of mind boggling, that's an eternity. Not that it's _really_ that important as this is a pretty niche driver, but still pretty ugly... Does it work reliably with a limit of 100 spins? If things get truly stuck, spinning forever in that loop is not going to help. In any case, your patch should have Cc: stable@vger.kernel.org Fixes: a11f6ca9aef9 ("sunvdc: Do not spin in an infinite loop when vio_ldc_send() returns EAGAIN") tags added. -- Jens Axboe