Re: [PATCH] parisc: Optimize per-pagetable spinlocks (v11)

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Jan 27, 2021 at 10:18:51PM +0100, Helge Deller wrote:
> On parisc a spinlock is stored in the next page behind the pgd which
> protects against parallel accesses to the pgd. That's why one additional
> page (PGD_ALLOC_ORDER) is allocated for the pgd.
> 
> Matthew Wilcox suggested that we instead should use a pointer in the
> struct page table for this spinlock and noted, that the comments for the
> PGD_ORDER and PMD_ORDER defines were wrong.
> 
> Both suggestions are addressed in this patch. The pgd spinlock
> (parisc_pgd_lock) is stored in the struct page table. In
> switch_mm_irqs_off() the physical address of this lock is loaded into
> cr28 (tr4) and the pgd into cr25, so that the fault handlers can
> directly access the lock.
> 
> The currently implemened Hybrid L2/L3 page table scheme (where the pmd
> is adjacent to the pgd) is dropped now too.
> 
> Suggested-by: Matthew Wilcox <willy@infradead.org>
> Fixes: b37d1c1898b2 ("parisc: Use per-pagetable spinlock")
> Signed-off-by: Helge Deller <deller@gmx.de>
> Signed-off-by: John David Anglin <dave.anglin@bell.net>

This patch results in:

BUG: spinlock recursion on CPU#0, swapper/0/1
 lock: 0x12226d14, .magic: dead4ead, .owner: swapper/0/1, .owner_cpu: 0
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.11.0-rc7-next-20210209-32bit #1
Hardware name: 9000/778/B160L
Backtrace:
 [<1019f9bc>] show_stack+0x34/0x48
 [<10a65278>] dump_stack+0x94/0x114
 [<10219f4c>] spin_dump+0x8c/0xb8
 [<1021a0b4>] do_raw_spin_lock+0xdc/0x108
 [<10a7367c>] _raw_spin_lock_irqsave+0x30/0x48
 [<102bf41c>] handle_mm_fault+0x5e8/0xdb0
 [<102b813c>] __get_user_pages.part.0+0x1b0/0x3d4
 [<102b8900>] __get_user_pages_remote+0x134/0x34c
 [<102b8b80>] get_user_pages_remote+0x68/0x90
 [<102fccb0>] get_arg_page+0x94/0xd8
 [<102fdd84>] copy_string_kernel+0xc4/0x234
 [<102fe70c>] kernel_execve+0xcc/0x1a4
 [<10a58d94>] run_init_process+0xbc/0xe0
 [<10a70d50>] kernel_init+0x98/0x13c
 [<1019a01c>] ret_from_kernel_thread+0x1c/0x24

when trying to boot parisc/hppa images in qemu. Reverting this patch fixes
the problem.

Bitsect log attached.

Guenter

---
# bad: [a4bfd8d46ac357c12529e4eebb6c89502b03ecc9] Add linux-next specific files for 20210209
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git bisect bad b68df186dae8ae890df08059bb068b78252b053a
# good: [323c9f6fb99b033883b404ecbc811e7b283a60b3] Merge remote-tracking branch 'sunxi/sunxi/for-next'
git bisect good 323c9f6fb99b033883b404ecbc811e7b283a60b3
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# good: [26418b36a11f2eaf2556aa8cefe86132907e311f] powerpc/64s/radix: refactor TLB flush type selection
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# bad: [d7bbb31642d2bd4aa5aad3595061a5e96c32d91d] Merge remote-tracking branch 'parisc-hd/for-next'
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# good: [2261352157a932717ec08b9dd18d1bfbb7c37c52] Merge remote-tracking branch 'openrisc/or1k-5.11-fixes' into or1k-5.12-updates
git bisect good 2261352157a932717ec08b9dd18d1bfbb7c37c52
# good: [3c92b9eed3ae088ade3688fb356a90926c1c8ee4] Merge remote-tracking branch 'openrisc/for-next'
git bisect good 3c92b9eed3ae088ade3688fb356a90926c1c8ee4
# good: [accb4993d2ee6b644a3d01851cf2fb2c1e0813a6] parisc: Fix IVT checksum calculation wrt HPMC
git bisect good accb4993d2ee6b644a3d01851cf2fb2c1e0813a6
# bad: [4add5f175b1e4e71c06493f9a2c52490d2ea4365] parisc: Optimize per-pagetable spinlocks
git bisect bad 4add5f175b1e4e71c06493f9a2c52490d2ea4365
# good: [0d2d3836dd0a597e514e6231fbf2ae3944f5d38c] parisc: Bump 64-bit IRQ stack size to 64 KB
git bisect good 0d2d3836dd0a597e514e6231fbf2ae3944f5d38c
# first bad commit: [4add5f175b1e4e71c06493f9a2c52490d2ea4365] parisc: Optimize per-pagetable spinlocks