Re: [PATCH AUTOSEL 4.14 6/6] ata: libata-eh: do not clear ATA_PFLAG_EH_PENDING in ata_eh_reset()

Hello Sasha,

The upstream commit that you are backporting here: 80cc944eca4f ("ata: libata-eh: do not clear ATA_PFLAG_EH_PENDING in ata_eh_reset()")

Requires that we have: 737dd811a3db ("ata: libahci: clear pending interrupt status") in stable. This is currently not the case.

See my comment in: https://lore.kernel.org/stable/ZRWf7Avtdv3DeqCU@x1-carbon/T/#t

Perhaps both: 93c7711494f4 ("ata: ahci: Drop pointless VPRINTK() calls and convert the remaining ones") and 737dd811a3db ("ata: libahci: clear pending interrupt status")

Could be backported to stable. That way, 80cc944eca4f ("ata: libata-eh: do not clear ATA_PFLAG_EH_PENDING in ata_eh_reset()") should be safe to backport to stable as well.

Kind regards, Niklas

On Sun, Sep 24, 2023 at 09:20:49AM -0400, Sasha Levin wrote:

From: Niklas Cassel niklas.cassel@wdc.com

[ Upstream commit 80cc944eca4f0baa9c381d0706f3160e491437f2 ]

ata_scsi_port_error_handler() starts off by clearing ATA_PFLAG_EH_PENDING, before calling ap->ops->error_handler() (without holding the ap->lock).

If an error IRQ is received while ap->ops->error_handler() is running, the irq handler will set ATA_PFLAG_EH_PENDING.

Once ap->ops->error_handler() returns, ata_scsi_port_error_handler() checks if ATA_PFLAG_EH_PENDING is set, and if it is, another iteration of ATA EH is performed.

The problem is that ATA_PFLAG_EH_PENDING is not only cleared by ata_scsi_port_error_handler(), it is also cleared by ata_eh_reset().

ata_eh_reset() is called by ap->ops->error_handler(). This additional clearing done by ata_eh_reset() breaks the whole retry logic in ata_scsi_port_error_handler(). Thus, if an error IRQ is received while ap->ops->error_handler() is running, the port will currently remain frozen and will never get re-enabled.

The additional clearing in ata_eh_reset() was introduced in commit 1e641060c4b5 ("libata: clear eh_info on reset completion").

Looking at the original error report: https://marc.info/?l=linux-ide&m=124765325828495&w=2

We can see the following happening: [ 1.074659] ata3: XXX port freeze [ 1.074700] ata3: XXX hardresetting link, stopping engine [ 1.074746] ata3: XXX flipping SControl

[ 1.411471] ata3: XXX irq_stat=400040 CONN|PHY [ 1.411475] ata3: XXX port freeze

[ 1.420049] ata3: XXX starting engine [ 1.420096] ata3: XXX rc=0, class=1 [ 1.420142] ata3: XXX clearing IRQs for thawing [ 1.420188] ata3: XXX port thawed [ 1.420234] ata3: SATA link up 3.0 Gbps (SStatus 123 SControl 300)

We are not supposed to be able to receive an error IRQ while the port is frozen (PxIE is set to 0, i.e. all IRQs for the port are disabled).

AHCI 1.3.1 section 10.7.1.1 First Tier (IS Register) states: "Each bit location can be thought of as reporting a '1' if the virtual "interrupt line" for that port is indicating it wishes to generate an interrupt. That is, if a port has one or more interrupt status bit set, and the enables for those status bits are set, then this bit shall be set."

Additionally, AHCI state P:ComInit clearly shows that the state machine will only jump to P:ComInitSetIS (which sets IS.IPS(x) to '1'), if PxIE.PCE is set to '1'. In our case, PxIE is set to 0, so IS.IPS(x) won't get set.

So IS.IPS(x) only gets set if PxIS and PxIE is set.

AHCI 1.3.1 section 10.7.1.1 First Tier (IS Register) also states: "The bits in this register are read/write clear. It is set by the level of the virtual interrupt line being a set, and cleared by a write of '1' from the software."

So if IS.IPS(x) is set, you need to explicitly clear it by writing a 1 to IS.IPS(x) for that port.

Since PxIE is cleared, the only way to get an interrupt while the port is frozen, is if IS.IPS(x) is set, and the only way IS.IPS(x) can be set when the port is frozen, is if it was set before the port was frozen.

However, since commit 737dd811a3db ("ata: libahci: clear pending interrupt status"), we clear both PxIS and IS.IPS(x) after freezing the port, but before the COMRESET, so the problem that commit 1e641060c4b5 ("libata: clear eh_info on reset completion") fixed can no longer happen.

Thus, revert commit 1e641060c4b5 ("libata: clear eh_info on reset completion"), so that the retry logic in ata_scsi_port_error_handler() works once again. (The retry logic is still needed, since we can still get an error IRQ _after_ the port has been thawed, but before ata_scsi_port_error_handler() takes the ap->lock in order to check if ATA_PFLAG_EH_PENDING is set.)

Signed-off-by: Niklas Cassel niklas.cassel@wdc.com Signed-off-by: Damien Le Moal dlemoal@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org

---

drivers/ata/libata-eh.c | 13 +++---------- 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c index cbe9af624a06f..8a789de056807 100644 --- a/drivers/ata/libata-eh.c +++ b/drivers/ata/libata-eh.c @@ -2948,18 +2948,11 @@ int ata_eh_reset(struct ata_link *link, int classify, postreset(slave, classes); }

• /*

• * Some controllers can't be frozen very well and may set spurious
  

• * error conditions during reset.  Clear accumulated error
  

• * information and re-thaw the port if frozen.  As reset is the
  

• * final recovery action and we cross check link onlineness against
  

• * device classification later, no hotplug event is lost by this.
  

• */
  

• /* clear cached SError */ spin_lock_irqsave(link->ap->lock, flags);

• memset(&link->eh_info, 0, sizeof(link->eh_info));

• link->eh_info.serror = 0; if (slave)

• memset(&slave->eh_info, 0, sizeof(link->eh_info));
  

• ap->pflags &= ~ATA_PFLAG_EH_PENDING;

• slave->eh_info.serror = 0;
  

  spin_unlock_irqrestore(link->ap->lock, flags);

if (ap->pflags & ATA_PFLAG_FROZEN) -- 2.40.1