1. 21 Jul, 2013 6 commits
    • Daniel Vetter's avatar
      drm/crtc-helper: explicit DPMS on after modeset · 25f397a4
      Daniel Vetter authored
      Atm the crtc helper implementation of set_config has really
      inconsisten semantics: If just an fb update is good enough, dpms state
      will be left as-is, but if we do a full modeset we force everything to
      dpms on.
      
      This change has already been applied to the i915 modeset code in
      
      commit e3de42b6
      Author: Imre Deak <imre.deak@intel.com>
      Date:   Fri May 3 19:44:07 2013 +0200
      
          drm/i915: force full modeset if the connector is in DPMS OFF mode
      
      which according to Greg KH seems to aim for a new record in most
      Bugzilla: links in a commit message.
      
      The history of this dpms forcing is pretty interesting. This patch
      here is an almost-revert of
      
      commit 811aaa55
      Author: Keith Packard <keithp@keithp.com>
      Date:   Thu Feb 3 16:57:28 2011 -0800
      
          drm: Only set DPMS ON when actually configuring a mode
      
      which fixed the bug of trying to dpms on disabled outputs, but
      introduced the new discrepancy between an fb update only and full
      modesets. The actual introduction of this goes back to
      
      commit bf9dc102
      Author: Keith Packard <keithp@keithp.com>
      Date:   Fri Nov 26 10:45:58 2010 -0800
      
          drm: Set connector DPMS status to ON in drm_crtc_helper_set_config
      
      And if you'd dig around in the i915 driver code there's even more fun
      around forcing dpms on and losing our heads and temper of the
      resulting inconsistencies. Especially the DP re-training code had tons
      of funny stuff in it.
      
      v2: So v1 totally blew up on resume on my radeon system here. After
      much head-scraching I've figured out that the radeon resume functions
      resumes the console system _before_ it actually restores all the
      modeset state. And resuming the console systems means that fbdev doeas
      an immediate ->set_par call.
      
      Now up to this patch that ->set_par did absolutely nothing: All the
      old sw state from pre-suspend was still around (since the modeset
      reset wasn't done yet), which means that the set_config calls done as
      a result of the ->set_par where all treated as no-ops (despite that
      the real hw state was obviously something completely different).
      
      Since v1 of this patch just added a bunch of ->dpms calls if the crtc
      was enabled, those set_config calls suddenly stopped being no-ops. But
      because the hw state wasn't restored the ->dpms callbacks resulted in
      decent amounts of hilarity and eventual full hangs.
      
      Since I can't review all kms drivers for such tricky ordering
      constraints v2 opts for a different approach and forces a full modeset
      if the connector dpms state isnt' DPMS_ON. Since the ->dpms callbacks
      implemented by the modeset helpers update the connector->dpms property
      we have the same effect of ensuring that the pipe is ultimately turned
      on, even if we just end up updating the fb. This is the same approac
      we ended up using in the intel driver.
      
      Note that besides i915.ko only all other drivers eventually call
      drm_helper_connector_dpms with the exception of vmwgfx, which does not
      support dmps at all.
      
      v3: Dave Airlie merged the broken first version of this patch, so
      squash in the revert of
      
      commit 372835a8
      Author: Daniel Vetter <daniel.vetter@ffwll.ch>
      Date:   Sat Jun 15 00:13:13 2013 +0200
      
          drm/crtc-helper: explicit DPMS on after modeset
      
      Also fix up the spelling fail a bit in the commit message while at it.
      
      Cc: Dave Airlie <airlied@redhat.com>
      Reviewed-by: default avatarAlex Deucher <alexdeucher@gmail.com>
      Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67043Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
      Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
      25f397a4
    • Linus Torvalds's avatar
      Linux 3.11-rc2 · 3b2f64d0
      Linus Torvalds authored
      3b2f64d0
    • Linus Torvalds's avatar
      Merge tag 'acpi-video-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm · ea45ea70
      Linus Torvalds authored
      Pull ACPI video support fixes from Rafael Wysocki:
       "I'm sending a separate pull request for this as it may be somewhat
        controversial.  The breakage addressed here is not really new and the
        fixes may not satisfy all users of the affected systems, but we've had
        so much back and forth dance in this area over the last several weeks
        that I think it's time to actually make some progress.
      
        The source of the problem is that about a year ago we started to tell
        BIOSes that we're compatible with Windows 8, which we really need to
        do, because some systems shipping with Windows 8 are tested with it
        and nothing else, so if we tell their BIOSes that we aren't compatible
        with Windows 8, we expose our users to untested BIOS/AML code paths.
      
        However, as it turns out, some Windows 8-specific AML code paths are
        not tested either, because Windows 8 actually doesn't use the ACPI
        methods containing them, so if we declare Windows 8 compatibility and
        attempt to use those ACPI methods, things break.  That occurs mostly
        in the backlight support area where in particular the _BCM and _BQC
        methods are plain unusable on some systems if the OS declares Windows
        8 compatibility.
      
        [ The additional twist is that they actually become usable if the OS
          says it is not compatible with Windows 8, but that may cause
          problems to show up elsewhere ]
      
        Investigation carried out by Matthew Garrett indicates that what
        Windows 8 does about backlight is to leave backlight control up to
        individual graphics drivers.  At least there's evidence that it does
        that if the Intel graphics driver is used, so we've decided to follow
        Windows 8 in that respect and allow i915 to control backlight (Daniel
        likes that part).
      
        The first commit from Aaron Lu makes ACPICA export the variable from
        which we can infer whether or not the BIOS believes that we are
        compatible with Windows 8.
      
        The second commit from Matthew Garrett prepares the ACPI video driver
        by making it initialize the ACPI backlight even if it is not going to
        be used afterward (that is needed for backlight control to work on
        Thinkpads).
      
        The third commit implements the actual workaround making i915 take
        over backlight control if the firmware thinks it's dealing with
        Windows 8 and is based on the work of multiple developers, including
        Matthew Garrett, Chun-Yi Lee, Seth Forshee, and Aaron Lu.
      
        The final commit from Aaron Lu makes us follow Windows 8 by informing
        the firmware through the _DOS method that it should not carry out
        automatic brightness changes, so that brightness can be controlled by
        GUI.
      
        Hopefully, this approach will allow us to avoid using blacklists of
        systems that should not declare Windows 8 compatibility just to avoid
        backlight control problems in the future.
      
         - Change from Aaron Lu makes ACPICA export a variable which can be
           used by driver code to determine whether or not the BIOS believes
           that we are compatible with Windows 8.
      
         - Change from Matthew Garrett makes the ACPI video driver initialize
           the ACPI backlight even if it is not going to be used afterward
           (that is needed for backlight control to work on Thinkpads).
      
         - Fix from Rafael J Wysocki implements Windows 8 backlight support
           workaround making i915 take over bakclight control if the firmware
           thinks it's dealing with Windows 8.  Based on the work of multiple
           developers including Matthew Garrett, Chun-Yi Lee, Seth Forshee,
           and Aaron Lu.
      
         - Fix from Aaron Lu makes the kernel follow Windows 8 by informing
           the firmware through the _DOS method that it should not carry out
           automatic brightness changes, so that brightness can be controlled
           by GUI"
      
      * tag 'acpi-video-3.11' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
        ACPI / video: no automatic brightness changes by win8-compatible firmware
        ACPI / video / i915: No ACPI backlight if firmware expects Windows 8
        ACPI / video: Always call acpi_video_init_brightness() on init
        ACPICA: expose OSI version
      ea45ea70
    • Linus Torvalds's avatar
      Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4 · 90db76e8
      Linus Torvalds authored
      Pull ext[34] tmpfile bugfix from Ted Ts'o:
       "Fix regression caused by commit af51a2ac which added ->tmpfile()
        support (along with a similar fix for ext3)"
      
      * tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
        ext3: fix a BUG when opening a file with O_TMPFILE flag
        ext4: fix a BUG when opening a file with O_TMPFILE flag
      90db76e8
    • Zheng Liu's avatar
      ext3: fix a BUG when opening a file with O_TMPFILE flag · dda5690d
      Zheng Liu authored
      When we try to open a file with O_TMPFILE flag, we will trigger a bug.
      The root cause is that in ext4_orphan_add() we check ->i_nlink == 0 and
      this check always fails because we set ->i_nlink = 1 in
      inode_init_always().  We can use the following program to trigger it:
      
      int main(int argc, char *argv[])
      {
      	int fd;
      
      	fd = open(argv[1], O_TMPFILE, 0666);
      	if (fd < 0) {
      		perror("open ");
      		return -1;
      	}
      	close(fd);
      	return 0;
      }
      
      The oops message looks like this:
      
      kernel: kernel BUG at fs/ext3/namei.c:1992!
      kernel: invalid opcode: 0000 [#1] SMP
      kernel: Modules linked in: ext4 jbd2 crc16 cpufreq_ondemand ipv6 dm_mirror dm_region_hash dm_log dm_mod parport_pc parport serio_raw sg dcdbas pcspkr i2c_i801 ehci_pci ehci_hcd button acpi_cpufreq mperf e1000e ptp pps_core ttm drm_kms_helper drm hwmon i2c_algo_bit i2c_core ext3 jbd sd_mod ahci libahci libata scsi_mod uhci_hcd
      kernel: CPU: 0 PID: 2882 Comm: tst_tmpfile Not tainted 3.11.0-rc1+ #4
      kernel: Hardware name: Dell Inc. OptiPlex 780 /0V4W66, BIOS A05 08/11/2010
      kernel: task: ffff880112d30050 ti: ffff8801124d4000 task.ti: ffff8801124d4000
      kernel: RIP: 0010:[<ffffffffa00db5ae>] [<ffffffffa00db5ae>] ext3_orphan_add+0x6a/0x1eb [ext3]
      kernel: RSP: 0018:ffff8801124d5cc8  EFLAGS: 00010202
      kernel: RAX: 0000000000000000 RBX: ffff880111510128 RCX: ffff8801114683a0
      kernel: RDX: 0000000000000000 RSI: ffff880111510128 RDI: ffff88010fcf65a8
      kernel: RBP: ffff8801124d5d18 R08: 0080000000000000 R09: ffffffffa00d3b7f
      kernel: R10: ffff8801114683a0 R11: ffff8801032a2558 R12: 0000000000000000
      kernel: R13: ffff88010fcf6800 R14: ffff8801032a2558 R15: ffff8801115100d8
      kernel: FS:  00007f5d172b5700(0000) GS:ffff880117c00000(0000) knlGS:0000000000000000
      kernel: CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
      kernel: CR2: 00007f5d16df15d0 CR3: 0000000110b1d000 CR4: 00000000000407f0
      kernel: Stack:
      kernel: 000000000000000c ffff8801048a7dc8 ffff8801114685a8 ffffffffa00b80d7
      kernel: ffff8801124d5e38 ffff8801032a2558 ffff88010ce24d68 0000000000000000
      kernel: ffff88011146b300 ffff8801124d5d44 ffff8801124d5d78 ffffffffa00db7e1
      kernel: Call Trace:
      kernel: [<ffffffffa00b80d7>] ? journal_start+0x8c/0xbd [jbd]
      kernel: [<ffffffffa00db7e1>] ext3_tmpfile+0xb2/0x13b [ext3]
      kernel: [<ffffffff821076f8>] path_openat+0x11f/0x5e7
      kernel: [<ffffffff821c86b4>] ? list_del+0x11/0x30
      kernel: [<ffffffff82065fa2>] ?  __dequeue_entity+0x33/0x38
      kernel: [<ffffffff82107cd5>] do_filp_open+0x3f/0x8d
      kernel: [<ffffffff82112532>] ? __alloc_fd+0x50/0x102
      kernel: [<ffffffff820f9296>] do_sys_open+0x13b/0x1cd
      kernel: [<ffffffff820f935c>] SyS_open+0x1e/0x20
      kernel: [<ffffffff82398c02>] system_call_fastpath+0x16/0x1b
      kernel: Code: 39 c7 0f 85 67 01 00 00 0f b7 03 25 00 f0 00 00 3d 00 40 00 00 74 18 3d 00 80 00 00 74 11 3d 00 a0 00 00 74 0a 83 7b 48 00 74 04 <0f> 0b eb fe 49 8b 85 50 03 00 00 4c 89 f6 48 c7 c7 c0 99 0e a0
      kernel: RIP  [<ffffffffa00db5ae>] ext3_orphan_add+0x6a/0x1eb [ext3]
      kernel: RSP <ffff8801124d5cc8>
      
      Here we couldn't call clear_nlink() directly because in d_tmpfile() we
      will call inode_dec_link_count() to decrease ->i_nlink.  So this commit
      tries to call d_tmpfile() before ext4_orphan_add() to fix this problem.
      Signed-off-by: default avatarZheng Liu <wenqing.lz@taobao.com>
      Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      dda5690d
    • Zheng Liu's avatar
      ext4: fix a BUG when opening a file with O_TMPFILE flag · e94bd349
      Zheng Liu authored
      When we try to open a file with O_TMPFILE flag, we will trigger a bug.
      The root cause is that in ext4_orphan_add() we check ->i_nlink == 0 and
      this check always fails because we set ->i_nlink = 1 in
      inode_init_always().  We can use the following program to trigger it:
      
      int main(int argc, char *argv[])
      {
      	int fd;
      
      	fd = open(argv[1], O_TMPFILE, 0666);
      	if (fd < 0) {
      		perror("open ");
      		return -1;
      	}
      	close(fd);
      	return 0;
      }
      
      The oops message looks like this:
      
      kernel BUG at fs/ext4/namei.c:2572!
      invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
      Modules linked in: dlci bridge stp hidp cmtp kernelcapi l2tp_ppp l2tp_netlink l2tp_core sctp libcrc32c rfcomm tun fuse nfnetli
      nk can_raw ipt_ULOG can_bcm x25 scsi_transport_iscsi ipx p8023 p8022 appletalk phonet psnap vmw_vsock_vmci_transport af_key vmw_vmci rose vsock atm can netrom ax25 af_rxrpc ir
      da pppoe pppox ppp_generic slhc bluetooth nfc rfkill rds caif_socket caif crc_ccitt af_802154 llc2 llc snd_hda_codec_realtek snd_hda_intel snd_hda_codec serio_raw snd_pcm pcsp
      kr edac_core snd_page_alloc snd_timer snd soundcore r8169 mii sr_mod cdrom pata_atiixp radeon backlight drm_kms_helper ttm
      CPU: 1 PID: 1812571 Comm: trinity-child2 Not tainted 3.11.0-rc1+ #12
      Hardware name: Gigabyte Technology Co., Ltd. GA-MA78GM-S2H/GA-MA78GM-S2H, BIOS F12a 04/23/2010
      task: ffff88007dfe69a0 ti: ffff88010f7b6000 task.ti: ffff88010f7b6000
      RIP: 0010:[<ffffffff8125ce69>]  [<ffffffff8125ce69>] ext4_orphan_add+0x299/0x2b0
      RSP: 0018:ffff88010f7b7cf8  EFLAGS: 00010202
      RAX: 0000000000000000 RBX: ffff8800966d3020 RCX: 0000000000000000
      RDX: 0000000000000000 RSI: ffff88007dfe70b8 RDI: 0000000000000001
      RBP: ffff88010f7b7d40 R08: ffff880126a3c4e0 R09: ffff88010f7b7ca0
      R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801271fd668
      R13: ffff8800966d2f78 R14: ffff88011d7089f0 R15: ffff88007dfe69a0
      FS:  00007f70441a3740(0000) GS:ffff88012a800000(0000) knlGS:00000000f77c96c0
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 0000000002834000 CR3: 0000000107964000 CR4: 00000000000007e0
      DR0: 0000000000780000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
      Stack:
       0000000000002000 00000020810b6dde 0000000000000000 ffff88011d46db00
       ffff8800966d3020 ffff88011d7089f0 ffff88009c7f4c10 ffff88010f7b7f2c
       ffff88007dfe69a0 ffff88010f7b7da8 ffffffff8125cfac ffff880100000004
      Call Trace:
       [<ffffffff8125cfac>] ext4_tmpfile+0x12c/0x180
       [<ffffffff811cba78>] path_openat+0x238/0x700
       [<ffffffff8100afc4>] ? native_sched_clock+0x24/0x80
       [<ffffffff811cc647>] do_filp_open+0x47/0xa0
       [<ffffffff811db73f>] ? __alloc_fd+0xaf/0x200
       [<ffffffff811ba2e4>] do_sys_open+0x124/0x210
       [<ffffffff81010725>] ? syscall_trace_enter+0x25/0x290
       [<ffffffff811ba3ee>] SyS_open+0x1e/0x20
       [<ffffffff816ca8d4>] tracesys+0xdd/0xe2
       [<ffffffff81001001>] ? start_thread_common.constprop.6+0x1/0xa0
      Code: 04 00 00 00 89 04 24 31 c0 e8 c4 77 04 00 e9 43 fe ff ff 66 25 00 d0 66 3d 00 80 0f 84 0e fe ff ff 83 7b 48 00 0f 84 04 fe ff ff <0f> 0b 49 8b 8c 24 50 07 00 00 e9 88 fe ff ff 0f 1f 84 00 00 00
      
      Here we couldn't call clear_nlink() directly because in d_tmpfile() we
      will call inode_dec_link_count() to decrease ->i_nlink.  So this commit
      tries to call d_tmpfile() before ext4_orphan_add() to fix this problem.
      Reported-by: default avatarDave Jones <davej@redhat.com>
      Signed-off-by: default avatarZheng Liu <wenqing.lz@taobao.com>
      Tested-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
      Tested-by: default avatarDave Jones <davej@redhat.com>
      Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
      Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      e94bd349
  2. 20 Jul, 2013 7 commits
    • Linus Torvalds's avatar
      Merge tag 'staging-3.11-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging · f6a0d9d5
      Linus Torvalds authored
      Pull staging tree fixes from Greg KH:
       "Here are a few iio driver fixes for 3.11-rc2.  They are still spread
        across drivers/iio and drivers/staging/iio so they are coming in
        through this tree.
      
        I've also removed the drivers/staging/csr/ driver as the developers
        who originally sent it to me have moved on to other companies, and CSR
        still will not send us the specs for the device, making the driver
        pretty much obsolete and impossible to fix up.  Deleting it now
        prevents people from sending in lots of tiny codingsyle fixes that
        will never go anywhere.
      
        It also helps to offset the large lustre filesystem merge that
        happened in 3.11-rc1 in the overall 3.11.0 diffstat.  :)"
      
      * tag 'staging-3.11-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging:
        staging: csr: remove driver
        iio: lps331ap: Fix wrong in_pressure_scale output value
        iio staging: fix lis3l02dq, read error handling
        staging:iio:ad7291: add missing .driver_module to struct iio_info
        iio: ti_am335x_adc: add missing .driver_module to struct iio_info
        iio: mxs-lradc: Remove useless check in read_raw
        iio: mxs-lradc: Fix misuse of iio->trig
        iio: inkern: fix iio_convert_raw_to_processed_unlocked
        iio: Fix iio_channel_has_info
        iio:trigger: device_unregister->device_del to avoid double free
        iio: dac: ad7303: fix error return code in ad7303_probe()
      f6a0d9d5
    • Linus Torvalds's avatar
      Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs · 36231d25
      Linus Torvalds authored
      Pull vfs fixes from Al Viro:
       "The sget() one is a long-standing bug and will need to go into -stable
        (in fact, it had been originally caught in RHEL6), the other two are
        3.11-only"
      
      * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
        vfs: constify dentry parameter in d_count()
        livelock avoidance in sget()
        allow O_TMPFILE to work with O_WRONLY
      36231d25
    • Linus Torvalds's avatar
      Merge tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4 · 19bf1c2c
      Linus Torvalds authored
      Pull ext4 bugfixes from Ted Ts'o:
       "Fixes for 3.11-rc2, sent at 5pm, in the professoinal style.  :-)"
      
      I'm not sure I like this new level of "professionalism".
      9-5, people, 9-5.
      
      * tag 'ext4_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
        ext4: call ext4_es_lru_add() after handling cache miss
        ext4: yield during large unlinks
        ext4: make the extent_status code more robust against ENOMEM failures
        ext4: simplify calculation of blocks to free on error
        ext4: fix error handling in ext4_ext_truncate()
      19bf1c2c
    • Linus Torvalds's avatar
      Merge tag 'nfs-for-3.11-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs · 3be542d4
      Linus Torvalds authored
      Pull NFS client bugfixes from Trond Myklebust:
       - Fix a regression against NFSv4 FreeBSD servers when creating a new
         file
       - Fix another regression in rpc_client_register()
      
      * tag 'nfs-for-3.11-3' of git://git.linux-nfs.org/projects/trondmy/linux-nfs:
        NFSv4: Fix a regression against the FreeBSD server
        SUNRPC: Fix another issue with rpc_client_register()
      3be542d4
    • Linus Torvalds's avatar
      Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next · 90290c4e
      Linus Torvalds authored
      Pull btrfs fixes from Josef Bacik:
       "I'm playing the role of Chris Mason this week while he's on vacation.
        There are a few critical fixes for btrfs here, all regressions and
        have been tested well"
      
      * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next:
        Btrfs: fix wrong write offset when replacing a device
        Btrfs: re-add root to dead root list if we stop dropping it
        Btrfs: fix lock leak when resuming snapshot deletion
        Btrfs: update drop progress before stopping snapshot dropping
      90290c4e
    • Peng Tao's avatar
      vfs: constify dentry parameter in d_count() · 24924a20
      Peng Tao authored
      so that it can be used in places like d_compare/d_hash
      without causing a compiler warning.
      Signed-off-by: default avatarPeng Tao <tao.peng@emc.com>
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      24924a20
    • Al Viro's avatar
      livelock avoidance in sget() · acfec9a5
      Al Viro authored
      Eric Sandeen has found a nasty livelock in sget() - take a mount(2) about
      to fail.  The superblock is on ->fs_supers, ->s_umount is held exclusive,
      ->s_active is 1.  Along comes two more processes, trying to mount the same
      thing; sget() in each is picking that superblock, bumping ->s_count and
      trying to grab ->s_umount.  ->s_active is 3 now.  Original mount(2)
      finally gets to deactivate_locked_super() on failure; ->s_active is 2,
      superblock is still ->fs_supers because shutdown will *not* happen until
      ->s_active hits 0.  ->s_umount is dropped and now we have two processes
      chasing each other:
      s_active = 2, A acquired ->s_umount, B blocked
      A sees that the damn thing is stillborn, does deactivate_locked_super()
      s_active = 1, A drops ->s_umount, B gets it
      A restarts the search and finds the same superblock.  And bumps it ->s_active.
      s_active = 2, B holds ->s_umount, A blocked on trying to get it
      ... and we are in the earlier situation with A and B switched places.
      
      The root cause, of course, is that ->s_active should not grow until we'd
      got MS_BORN.  Then failing ->mount() will have deactivate_locked_super()
      shut the damn thing down.  Fortunately, it's easy to do - the key point
      is that grab_super() is called only for superblocks currently on ->fs_supers,
      so it can bump ->s_count and grab ->s_umount first, then check MS_BORN and
      bump ->s_active; we must never increment ->s_count for superblocks past
      ->kill_sb(), but grab_super() is never called for those.
      
      The bug is pretty old; we would've caught it by now, if not for accidental
      exclusion between sget() for block filesystems; the things like cgroup or
      e.g. mtd-based filesystems don't have anything of that sort, so they get
      bitten.  The right way to deal with that is obviously to fix sget()...
      Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      acfec9a5
  3. 19 Jul, 2013 27 commits