From: Thierry Reding <thierry.reding@gmail.com>
To: Sourav Poddar <sourav.poddar@ti.com>
Cc: linux-pwm@vger.kernel.org, linux-omap@vger.kernel.org, balbi@ti.com
Subject: Re: [PATCH 1/3] pwm: core: Rearrange pwm lock.
Date: Thu, 23 Jan 2014 14:54:50 +0100 [thread overview]
Message-ID: <20140123135449.GA6503@ulmo.nvidia.com> (raw)
In-Reply-To: <1387366615-23182-2-git-send-email-sourav.poddar@ti.com>
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On Wed, Dec 18, 2013 at 05:06:53PM +0530, Sourav Poddar wrote:
> When tiecap is used as a module, then while doing a rmmod I
> get the following dump.
>
> root@am437x-evm:/# rmmod pwm_tiecap
> [ 219.539245]
> [ 219.540771] ======================================================
> [ 219.546936] [ INFO: possible circular locking dependency detected ]
> [ 219.553192] 3.12.4-01557-g9921cde-dirty #134 Not tainted
> [ 219.558471] -------------------------------------------------------
> [ 219.564727] rmmod/1517 is trying to acquire lock:
> [ 219.569427] (s_active#35){++++.+}, at: [<c017ab00>] sysfs_hash_and_remove+0x4c/0x8c
> [ 219.577239]
> [ 219.577239] but task is already holding lock:
> [ 219.583068] (pwm_lock){+.+.+.}, at: [<c0303598>] pwmchip_remove+0x14/0xf8
> [ 219.589996]
> [ 219.589996] which lock already depends on the new lock.
> [ 219.589996]
> [ 219.598144]
> [ 219.598144] the existing dependency chain (in reverse order) is:
> [ 219.605590]
> -> #1 (pwm_lock){+.+.+.}:
> [ 219.609497] [<c00a2d1c>] lock_acquire+0x9c/0x128
> [ 219.614746] [<c0639bc0>] mutex_lock_nested+0x50/0x3dc
> [ 219.620391] [<c0303974>] pwm_request_from_chip+0x38/0x6c
> [ 219.626312] [<c0303fe0>] pwm_export_store+0x50/0x140
> [ 219.631896] [<c039aba8>] dev_attr_store+0x18/0x24
> [ 219.637207] [<c017aff0>] sysfs_write_file+0x16c/0x1a0
> [ 219.642883] [<c0119084>] vfs_write+0xb0/0x188
> [ 219.647857] [<c0119478>] SyS_write+0x3c/0x70
> [ 219.652770] [<c0014100>] ret_fast_syscall+0x0/0x48
> [ 219.658172]
> -> #0 (s_active#35){++++.+}:
> [ 219.662353] [<c00a2778>] __lock_acquire+0x1b28/0x1b70
> [ 219.667999] [<c00a2d1c>] lock_acquire+0x9c/0x128
> [ 219.673248] [<c017c780>] sysfs_addrm_finish+0xe8/0x158
> [ 219.678985] [<c017ab00>] sysfs_hash_and_remove+0x4c/0x8c
> [ 219.684906] [<c017e224>] remove_files+0x38/0x74
> [ 219.690063] [<c017e2a4>] sysfs_remove_group+0x44/0x108
> [ 219.695800] [<c017e38c>] sysfs_remove_groups+0x24/0x34
> [ 219.701538] [<c039bc2c>] device_del+0xec/0x178
> [ 219.706604] [<c039bcc4>] device_unregister+0xc/0x18
> [ 219.712097] [<c0303658>] pwmchip_remove+0xd4/0xf8
> [ 219.717407] [<c039fdc4>] platform_drv_remove+0x18/0x1c
> [ 219.723175] [<c039e6c4>] __device_release_driver+0x70/0xc8
> [ 219.729248] [<c039eec8>] driver_detach+0xb4/0xb8
> [ 219.734497] [<c039e4ec>] bus_remove_driver+0x8c/0xd0
> [ 219.740081] [<c00abd2c>] SyS_delete_module+0x118/0x22c
> [ 219.745819] [<c0014100>] ret_fast_syscall+0x0/0x48
> [ 219.751220]
> [ 219.751220] other info that might help us debug this:
> [ 219.751220]
> [ 219.759216] Possible unsafe locking scenario:
> [ 219.759216]
> [ 219.765106] CPU0 CPU1
> [ 219.769622] ---- ----
> [ 219.774139] lock(pwm_lock);
> [ 219.777130] lock(s_active#35);
> [ 219.782897] lock(pwm_lock);
> [ 219.788391] lock(s_active#35);
> [ 219.791656]
> [ 219.791656] *** DEADLOCK ***
> [ 219.791656]
> [ 219.797546] 3 locks held by rmmod/1517:
> [ 219.801391] #0: (&__lockdep_no_validate__){......}, at: [<c039ee58>] driver_detach+0x44/0xb8
> [ 219.810028] #1: (&__lockdep_no_validate__){......}, at: [<c039ee64>] driver_detach+0x50/0xb8
> [ 219.818695] #2: (pwm_lock){+.+.+.}, at: [<c0303598>] pwmchip_remove+0x14/0xf8
> [ 219.826049]
> [ 219.826049] stack backtrace:
> [ 219.830413] CPU: 0 PID: 1517 Comm: rmmod Not tainted 3.12.4-01557-g9921cde-dirty #134
> [ 219.838256] [<c001cc98>] (unwind_backtrace+0x0/0xf0) from [<c0018124>] (show_stack+0x10/0x14)
> [ 219.846771] [<c0018124>] (show_stack+0x10/0x14) from [<c0636728>] (dump_stack+0x74/0xb4)
> [ 219.854858] [<c0636728>] (dump_stack+0x74/0xb4) from [<c06344e4>] (print_circular_bug+0x284/0x2d8)
> [ 219.863830] [<c06344e4>] (print_circular_bug+0x284/0x2d8) from [<c00a2778>] (__lock_acquire+0x1b28/0x1b70)
> [ 219.873443] [<c00a2778>] (__lock_acquire+0x1b28/0x1b70) from [<c00a2d1c>] (lock_acquire+0x9c/0x128)
> [ 219.882476] [<c00a2d1c>] (lock_acquire+0x9c/0x128) from [<c017c780>] (sysfs_addrm_finish+0xe8/0x158)
> [ 219.891601] [<c017c780>] (sysfs_addrm_finish+0xe8/0x158) from [<c017ab00>] (sysfs_hash_and_remove+0x4c/0x8c)
> [ 219.901397] [<c017ab00>] (sysfs_hash_and_remove+0x4c/0x8c) from [<c017e224>] (remove_files+0x38/0x74)
> [ 219.910614] [<c017e224>] (remove_files+0x38/0x74) from [<c017e2a4>] (sysfs_remove_group+0x44/0x108)
> [ 219.919647] [<c017e2a4>] (sysfs_remove_group+0x44/0x108) from [<c017e38c>] (sysfs_remove_groups+0x24/0x34)
> [ 219.929260] [<c017e38c>] (sysfs_remove_groups+0x24/0x34) from [<c039bc2c>] (device_del+0xec/0x178)
> [ 219.938201] [<c039bc2c>] (device_del+0xec/0x178) from [<c039bcc4>] (device_unregister+0xc/0x18)
> [ 219.946899] [<c039bcc4>] (device_unregister+0xc/0x18) from [<c0303658>] (pwmchip_remove+0xd4/0xf8)
> [ 219.955841] [<c0303658>] (pwmchip_remove+0xd4/0xf8) from [<c039fdc4>] (platform_drv_remove+0x18/0x1c)
> [ 219.965057] [<c039fdc4>] (platform_drv_remove+0x18/0x1c) from [<c039e6c4>] (__device_release_driver+0x70/0xc8)
> [ 219.975006] [<c039e6c4>] (__device_release_driver+0x70/0xc8) from [<c039eec8>] (driver_detach+0xb4/0xb8)
> [ 219.984466] [<c039eec8>] (driver_detach+0xb4/0xb8) from [<c039e4ec>] (bus_remove_driver+0x8c/0xd0)
> [ 219.993438] [<c039e4ec>] (bus_remove_driver+0x8c/0xd0) from [<c00abd2c>] (SyS_delete_module+0x118/0x22c)
> [ 220.002899] [<c00abd2c>] (SyS_delete_module+0x118/0x22c) from [<c0014100>] (ret_fast_syscall+0x0/0x48)
>
> Looks like s_active lock cannot be held while pwm lock is held.
> The patch fixes the above issue by unlocking the pwm lock before acquiring the
> sysfs lock.
I've been trying to reproduce this, but I can't. I've enabled LOCKDEP
and PROVE_LOCKING in Kconfig, booted a Tegra-based board and did a
couple of modprobe pwm-tegra && modprobe -r pwm-tegra. But I never saw
LOCKDEP complain.
Can you reproduce the issue on latest linux-next? Or is there something
else I should be doing to trigger this?
Thierry
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next prev parent reply other threads:[~2014-01-23 13:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-18 11:36 [PATCH 0/3] pwm: ti: Miscellaneous Fixes and cleanup for pwm Sourav Poddar
2013-12-18 11:36 ` [PATCH 1/3] pwm: core: Rearrange pwm lock Sourav Poddar
2014-01-23 13:54 ` Thierry Reding [this message]
2013-12-18 11:36 ` [PATCH 2/3] driver: pwm: ti-ecap: Remove duplicate put_sync call Sourav Poddar
2014-01-23 14:19 ` Thierry Reding
2013-12-18 11:36 ` [PATCH 3/3] driver: pwmss: Disable stop clk bit during enable clock call Sourav Poddar
2014-01-23 14:17 ` Thierry Reding
2014-01-08 6:47 ` [PATCH 0/3] pwm: ti: Miscellaneous Fixes and cleanup for pwm sourav
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