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2006-12-04[S390] cpu shutdown reworkHeiko Carstens
Let one master cpu kill all other cpus instead of sending an external interrupt to all other cpus so they can kill themselves. Simplifies reipl/shutdown functions a lot. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] cpcmd <-> __cpcmd calling issuesHeiko Carstens
In case of reipl cpcmd gets called when all other cpus are not running anymore. To prevent deadlocks change __cpcmd so that it doesn't take any locks and call cpcmd or __cpcmd, whatever is correct in the current context. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Bad kexec control page allocation.Heiko Carstens
KEXEC_CONTROL_MEMORY_LIMIT is an unsigned long value and therefore should be defined as one. Otherwise the kexec control page can be allocated above 2GB which will cause a specification exception on the sam31 instruction in the s390 kexec relocation code. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Reset infrastructure for re-IPL.Heiko Carstens
In case of re-IPL and diag308 doesn't work we have to reset all devices manually and wait synchronously that each reset finished. This patch adds the necessary infrastucture and the first exploiter of it. Subsystems that need to add a function that needs to be called at re-IPL may register/unregister this function via struct reset_call { struct reset_call *next; void (*fn)(void); }; void register_reset_call(struct reset_call *reset); void unregister_reset_call(struct reset_call *reset); When the registered function get called the context is: - all cpus beside the current one are stopped - all machine checks and interrupts are disabled - prefixing is disabled - a default machine check handler is available for use The registered functions may not take any locks are sleep. For the common I/O layer part of this patch: Introduce a reset_call css_reset that does the following: - clear all subchannels - perform a rchp on all channel paths and wait for the resulting machine checks This replaces the calls to clear_all_subchannels() and cio_reset_channel_paths() for kexec and ccw reipl. reipl_ccw_dev() now uses reipl_find_schid() to determine the subchannel id for a given device id. Also remove cio_reset_channel_paths() and friends since they are not needed anymore. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Some documentation typos.Nicolas Kaiser
Signed-off-by: Nicolas Kaiser <nikai@nikai.net> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] extmem unbalanced spin_lock.Heiko Carstens
segment save will exit with a lock held if the passed segment doesn't exist. Any subsequent call to segment_save will lead to a deadlock. Fix this and give up the lock before returning. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] return 'count' for successful execution of dasd_eer_enable.Horst Hummel
Currently the return value of 'dasd_eer_enable' is returned - even if the function returned '0'. Now return 'count' for successful execution. Signed-off-by: Horst Hummel <horst.hummel@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Enhanced handling of failed termination requests.Horst Hummel
In case a request timed out and termination did not work, the console was flooded with retry messages (every 1/10s). Now we use a 5s delay per retry and generate a more precise message. Signed-off-by: Horst Hummel <horst.hummel@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Use diag instead of ccw reipl.Michael Holzheu
Since the diag 308 reipl method is superior to the ccw method, we should use it whenever it is possible. We can do that, if the user has not specified a new reipl ccw device and the system has been ipled from a ccw device. Signed-off-by: Michael Holzheu <holzheu@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Add MODALIAS= to the uevent for the ap bus.Cornelia Huck
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] 3215 device locking.Martin Schwidefsky
Remove lock pointer from 3215 device structure. Use get_ccwdev_lock for each use of the lock in the ccw-device structure. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] No panic for failed rebootMichael Holzheu
If reboot fails (e.g. because wrong devno has been specified by the user), we should just stop all cpus, but should not trigger a kernel panic. Signed-off-by: Michael Holzheu <holzheu@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] termio <-> termios conversion error handling.Heiko Carstens
Get rid of our own user_termio_to_kernel_termios() and kernel_termios_to_user_termio() macros which didn't check for errors on user space accesses. Instead use the generic functions which handle this properly. In addition the generic version of user_termio_to_kernel_termios() also copies the c_line member which was missing in our variant. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] update interface notes in zcrypt.hRalph Wuerthner
Signed-off-by: Ralph Wuerthner <rwuerthn@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Add ipl/reipl loadparm attribute.Michael Holzheu
If multiple kernel images are installed on one DASD, the loadparm can be used to select the boot configuration. This patch introduces the following two new sysfs attributes: /sys/firmware/ipl/loadparm: shows loadparm of current system (ro) /sys/firmware/reipl/ccw/loadparm: loadparm used for next reboot (rw) Signed-off-by: Michael Holzheu <holzheu@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Add __must_check to uaccess functions.Heiko Carstens
Follow other architectures and add __must_check to uaccess functions. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] Remove unused GENERIC_BUST_SPINLOCK from Kconfig.Heiko Carstens
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] handle incorrect values when writing to dasd sysfs attributes.Horst Hummel
When writing to dasd attributes (e.g. readonly), all values besides '1' are handled like '0'. Other sysfs-attributes like 'online' are checking for '1' and for '0' and do not accept other values. Therefore enhanced checking and error handling in dasd_devmap attribute store functions. Signed-off-by: Horst Hummel <horst.hummel@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[S390] remove salipl memory detection.Christian Borntraeger
The SALIPL entry point has an needless memory detection routine as we later check the memory size again. The SALIPL code also uses diagnose 0x060 if we are running under VM, but this diagnose is not compatible with the 64 bit addressing mode. The solution is to get rid of this code and rely on the memory detection in the startup code. Signed-off-by: Christian Borntraeger <cborntra@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
2006-12-04[PATCH] severing poll.h -> mm.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing skbuff.h -> mm.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing skbuff.h -> poll.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing skbuff.h -> highmem.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing uaccess.h -> sched.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing fs.h, radix-tree.h -> sched.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[PATCH] severing module.h->sched.hAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2006-12-04[SUNHME]: Fix for sunhme failures on x86Jurij Smakov
The following patch fixes the failure of sunhme drivers on x86 hosts due to missing pci_enable_device() and pci_set_master() calls, lost during code refactoring. It has been filed as bugzilla bug #7502 [0] and Debian bug #397460 [1]. [0] http://bugzilla.kernel.org/show_bug.cgi?id=7502 [1] http://bugs.debian.org/397460 Signed-off-by: Jurij Smakov <jurij@wooyd.org> Signed-off-by: David S. Miller <davem@davemloft.net>
2006-12-04Merge master.kernel.org:/pub/scm/linux/kernel/git/acme/net-2.6David S. Miller
2006-12-04Remove long-unmaintained ftape driver subsystem.Jeff Garzik
It's bitrotten, long unmaintained, long hidden under BROKEN_ON_SMP, etc. As scheduled in feature-removal-schedule.txt, and ack'd several times on lkml. Signed-off-by: Jeff Garzik <jeff@garzik.org>
2006-12-04[XFRM] xfrm_user: Better validation of user templates.David S. Miller
Since we never checked the ->family value of templates before, many applications simply leave it at zero. Detect this and fix it up to be the pol->family value. Also, do not clobber xp->family while reading in templates, that is not necessary. Signed-off-by: David S. Miller <davem@davemloft.net>
2006-12-03[DCCP] tfrc: Binary search for reverse TFRC lookupGerrit Renker
This replaces the linear search algorithm for reverse lookup with binary search. It has the advantage of better scalability: O(log2(N)) instead of O(N). This means that the average number of iterations is reduced from 250 (linear search if each value appears equally likely) down to at most 9. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] ccid3: Deprecate TFRC_SMALLEST_PGerrit Renker
This patch deprecates the existing use of an arbitrary value TFRC_SMALLEST_P for low-threshold values of p. This avoids masking low-resolution errors. Instead, the code now checks against real boundaries (implemented by preceding patch) and provides warnings whenever a real value falls below the threshold. If such messages are observed, it is a better solution to take this as an indication that the lookup table needs to be re-engineered. Changelog: ---------- This patch * makes handling all TFRC resolution errors local to the TFRC library * removes unnecessary test whether X_calc is 'infinity' due to p==0 -- this condition is already caught by tfrc_calc_x() * removes setting ccid3hctx_p = TFRC_SMALLEST_P in ccid3_hc_tx_packet_recv since this is now done by the TFRC library * updates BUG_ON test in ccid3_hc_tx_no_feedback_timer to take into account that p now is either 0 (and then X_calc is irrelevant), or it is > 0; since the handling of TFRC_SMALLEST_P is now taken care of in the tfrc library Justification: -------------- The TFRC code uses a lookup table which has a bounded resolution. The lowest possible value of the loss event rate `p' which can be resolved is currently 0.0001. Substituting this lower threshold for p when p is less than 0.0001 results in a huge, exponentially-growing error. The error can be computed by the following formula: (f(0.0001) - f(p))/f(p) * 100 for p < 0.0001 Currently the solution is to use an (arbitrary) value TFRC_SMALLEST_P = 40 * 1E-6 = 0.00004 and to consider all values below this value as `virtually zero'. Due to the exponentially growing resolution error, this is not a good idea, since it hides the fact that the table can not resolve practically occurring cases. Already at p == TFRC_SMALLEST_P, the error is as high as 58.19%! Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] tfrc: Identify TFRC table limits and simplify codeGerrit Renker
This * adds documentation about the lowest resolution that is possible within the bounds of the current lookup table * defines a constant TFRC_SMALLEST_P which defines this resolution * issues a warning if a given value of p is below resolution * combines two previously adjacent if-blocks of nearly identical structure into one This patch does not change the algorithm as such. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] tfrc: Add protection against invalid parameters to TFRC routinesGerrit Renker
1) For the forward X_calc lookup, it * protects effectively against RTT=0 (this case is possible), by returning the maximal lookup value instead of just setting it to 1 * reformulates the array-bounds exceeded condition: this only happens if p is greater than 1E6 (due to the scaling) * the case of negative indices can now with certainty be excluded, since documentation shows that the formulas are within bounds * additional protection against p = 0 (would give divide-by-zero) 2) For the reverse lookup, it warns against * protects against exceeding array bounds * now returns 0 if f(p) = 0, due to function definition * warns about minimal resolution error and returns the smallest table value instead of p=0 [this would mask congestion conditions] Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] tfrc: Fix small error in reverse lookup of p for given f(p)Gerrit Renker
This fixes the following small error in tfrc_calc_x_reverse_lookup. 1) The table is generated by the following equations: lookup[index][0] = g((index+1) * 1000000/TFRC_CALC_X_ARRSIZE); lookup[index][1] = g((index+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE); where g(q) is 1E6 * f(q/1E6) 2) The reverse lookup assigns an entry in lookup[index][small] 3) This index needs to match the above, i.e. * if small=0 then p = (index + 1) * 1000000/TFRC_CALC_X_ARRSIZE * if small=1 then p = (index+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE These are exactly the changes that the patch makes; previously the code did not conform to the way the lookup table was generated (this difference resulted in a mean error of about 1.12%). Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] tfrc: Document boundaries and limits of the TFRC lookup tableGerrit Renker
This adds documentation for the TCP Reno throughput equation which is at the heart of the TFRC sending rate / loss rate calculations. It spells out precisely how the values were determined and what they mean. The equations were derived through reverse engineering and found to be fully accurate (verified using test programs). This patch does not change any code. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] ccid3: Fix warning message about illegal ACKGerrit Renker
This avoids a (harmless) warning message being printed at the DCCP server (the receiver of a DCCP half connection). Incoming packets are both directed to * ccid_hc_rx_packet_recv() for the server half * ccid_hc_tx_packet_recv() for the client half The message gets printed since on a server the client half is currently not sending data packets. This is resolved for the moment by checking the DCCP-role first. In future times (bidirectional DCCP connections), this test may have to be more sophisticated. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP] ccid3: Fix bug in calculation of send rateGerrit Renker
The main object of this patch is the following bug: ==> In ccid3_hc_tx_packet_recv, the parameters p and X_recv were updated _after_ the send rate was calculated. This is clearly an error and is resolved by re-ordering statements. In addition, * r_sample is converted from u32 to long to check whether the time difference was negative (it would otherwise be converted to a large u32 value) * protection against RTT=0 (this is possible) is provided in a further patch * t_elapsed is also converted to long, to match the type of r_sample * adds a a more debugging information regarding current send rates * various trivial comment/documentation updates Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Acked-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP]: Fix BUG in retransmission delay calculationGerrit Renker
This bug resulted in ccid3_hc_tx_send_packet returning negative delay values, which in turn triggered silently dequeueing packets in dccp_write_xmit. As a result, only a few out of the submitted packets made it at all onto the network. Occasionally, when dccp_wait_for_ccid was involved, this also triggered a bug warning since ccid3_hc_tx_send_packet returned a negative value (which in reality was a negative delay value). The cause for this bug lies in the comparison if (delay >= hctx->ccid3hctx_delta) return delay / 1000L; The type of `delay' is `long', that of ccid3hctx_delta is `u32'. When comparing negative long values against u32 values, the test returned `true' whenever delay was smaller than 0 (meaning the packet was overdue to send). The fix is by casting, subtracting, and then testing the difference with regard to 0. This has been tested and shown to work. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Ian McDonald <ian.mcdonald@jandi.co.nz> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[DCCP]: Use higher RTO default for CCID3Gerrit Renker
The TFRC nofeedback timer normally expires after the maximum of 4 RTTs and twice the current send interval (RFC 3448, 4.3). On LANs with a small RTT this can mean a high processing load and reduced performance, since then the nofeedback timer is triggered very frequently. This patch provides a configuration option to set the bound for the nofeedback timer, using as default 100 milliseconds. By setting the configuration option to 0, strict RFC 3448 behaviour can be enforced for the nofeedback timer. Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk> Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
2006-12-03[PATCH] sata_promise: PHYMODE4 fixupMikael Pettersson
This patch adds code to fix up the PHYMODE4 "align timing" register value on second-generation Promise SATA chips. Failure to correct this value on non-x86 machines makes drive detection prone to failure due to timeouts. (I've observed about 50% detection failure rates on SPARC64.) The HW boots with a bad value in this register, but on x86 machines the Promise BIOS corrects it to the value recommended by the manual, so most people have been unaffected by this issue. After developing the patch I checked Promise's SATAII driver, and discovered that it also corrects PHYMODE4 just like this patch does. This patch depends on the sata_promise SATAII updates patch I sent recently. Signed-off-by: Mikael Pettersson <mikpe@it.uu.se> Signed-off-by: Jeff Garzik <jeff@garzik.org>
2006-12-03[PATCH] libata: always use polling IDENTIFYTejun Heo
libata switched to IRQ-driven IDENTIFY when IRQ-driven PIO was introduced. This has caused a lot of problems including device misdetection and phantom device. ATA_FLAG_DETECT_POLLING was added recently to selectively use polling IDENTIFY on problemetic drivers but many controllers and devices are affected by this problem and trying to adding ATA_FLAG_DETECT_POLLING for each such case is diffcult and not very rewarding. This patch makes libata always use polling IDENTIFY. This is consistent with libata's original behavior and drivers/ide's behavior. Signed-off-by: Tejun Heo <htejun@gmail.com> Signed-off-by: Jeff Garzik <jeff@garzik.org>
2006-12-03[libata] pata_cs5535: fix buildJeff Garzik
Noticed by Tejun and others. Signed-off-by: Jeff Garzik <jeff@garzik.org>
2006-12-03[PATCH] ahci: do not powerdown during initializationTejun Heo
ahci_init_controller() calls ahci_deinit_port() to make sure the controller is stopped before initializing the controller. In turn, ahci_deinit_port() invokes ahci_power_down() to power down the port. If the controller supports slumber mode, the link is put into it. Unfortunately, some devices don't implement link powersaving mode properly and show erratic behavior after link is put into slumber mode. For example, HL-DT-ST DVD-RAM GSA-H30N completely locks up on slumber transition and can only be recovered with the *REAL* hard reset - power removal and reapply. Note that this makes the first probing reset different from all others. If the above dvd-ram is hotplugged after ahci is initialized, no problem occurs because ahci is already fully initialized with phy powered up. So, this might also be the reason for other weird AHCI initial probing abnormalities. This patch moves power up/down out of port init/deinit and call them only when needed. Power down is now called only when suspending. As system suspend usually involves powering down 12v for storage devices, this shouldn't cause problem even if the attached device doesn't support slumber mode. However, in partial power management and suspend failure cases, devices might lock up after suspend attempt. I thought about removing transition to slumber mode altogether but ahci spec mandates it before HBA D3 state transition. Blacklisting such devices might be the solution. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: prepare ata_sg_clean() for invocation from EHTejun Heo
Make ata_sg_clean() global and don't allow NCQ for internal commands. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: separate out rw ATA taskfile building into ata_build_rw_tf()Tejun Heo
Separate out rw ATA taskfile building from ata_scsi_rw_xlat() into ata_build_rw_tf(). This will be used to improve media error handling. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: implement ata_exec_internal_sg()Tejun Heo
Sg'ify ata_exec_internal() and call it ata_exec_internal_sg(). Wrapper function around ata_exec_internal_sg() is implemented to provide ata_exec_internal() interface. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: make sure IRQ is cleared after ata_bmdma_freeze()Tejun Heo
Now that BMDMA status is recorded in irq handler. ata_bmdma_freeze() is free to manipulate host status. Under certain circumstances, some controllers (ICH7 in enhanced mode w/ IRQ shared) raise IRQ when CTL register is written to and ATA_NIEN doesn't mask it. This patch makes ata_bmdma_freeze() clear all pending IRQs after freezing a port. This change makes explicit clearing in ata_device_add() unnecessary and thus kills it. The removed code was SFF-specific and was in the wrong place. Note that ->freeze() handler is always called under ap->lock held and irq disabled. Even if CTL manipulation causes stuck IRQ, it's cleared immediately. This should be safe (enough) even in SMP environment. More correct solution is to mask the IRQ from IRQ controller but that would be an overkill. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: move BMDMA host status recording from EH to interrupt handlerTejun Heo
For certain errors, interrupt handler alter BMDMA host status before entering EH (clears active and intr). Thus altered BMDMA host status value is recorded by BMDMA EH and reported to user. Move BMDMA host status recording from EH to interrupt handler. Signed-off-by: Tejun Heo <htejun@gmail.com>
2006-12-03[PATCH] libata: make sure sdev doesn't go away while rescanningTejun Heo
ata_scsi_dev_rescan() doesn't synchronize against SCSI device detach and the target sdev might go away in the middle. Fix it. Signed-off-by: Tejun Heo <htejun@gmail.com>