Re: [PATCH v4 07/23] mailbox: Add RISC-V SBI message proxy (MPXY) based mailbox driver

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Wed, Jun 11, 2025 at 10:51:15AM +0530, Anup Patel wrote:
> On Tue, Jun 10, 2025 at 3:25 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> > On Tue, Jun 10, 2025 at 10:05:27AM +0530, Anup Patel wrote:
> > > On Tue, Jun 10, 2025 at 1:34 AM Andy Shevchenko
> > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > On Mon, Jun 09, 2025 at 05:59:40PM +0530, Anup Patel wrote:
> > > > > On Wed, May 28, 2025 at 4:23 PM Andy Shevchenko
> > > > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > > > On Sun, May 25, 2025 at 02:16:54PM +0530, Anup Patel wrote:

...

> > > > > > > +     if (mbox->msi_count)
> > > > > >
> > > > > > Is this check really needed?
> > > > >
> > > > > MSIs are optional for the SBI MPXY mailbox so we should only use
> > > > > platform_device_msi_xyz() APIs only when MSIs are available.
> > > >
> > > > > > > +             platform_device_msi_free_irqs_all(mbox->dev);
> > > >
> > > > Hmm... I am not sure why. Do you have any Oops or warnings if the check
> > > > is not there and no MSI provided?
> > >
> > > We don't see any oops or warnings. This check is to avoid unnecessary
> > > work (such as acquiring lock, checking default domain, etc) in the
> > > msi_domain_free_irqs_all() called by platform_device_msi_free_irqs_all().
> > >
> > > I don't mind dropping the check so I will update in the next revision.
> >
> > Perhaps you can rather add this check into the callee? Seems to me that
> > you have a justification for it. Usual pattern in the kernel that freeing
> > resources should be aware of the NULL pointers or optional resources
> > so we may call it unconditionally from the user(s).
> >
> 
> Unconditionally calling platform_device_msi_free_irqs_all() when there
> were no MSIs allocated causes the below crash because "dev->msi.data"
> is non-NULL only when:
> 
> [    1.355735] Unable to handle kernel NULL pointer dereference at
> virtual address 0000000000000008
> [    1.358212] Current swapper/0 pgtable: 4K pagesize, 57-bit VAs,
> pgdp=0x0000000081a2b000
> [    1.360632] [0000000000000008] pgd=0000000000000000
> [    1.363132] Oops [#1]
> [    1.363748] Modules linked in:
> [    1.364768] CPU: 3 UID: 0 PID: 1 Comm: swapper/0 Not tainted
> 6.16.0-rc1-00037-gab55e1c1d97a-dirty #7 NONE
> [    1.368325] epc : mutex_lock+0x0/0x28
> [    1.369796]  ra : __msi_lock_descs+0x32/0x3c
> [    1.370234] epc : ffffffff80af96e8 ra : ffffffff800038e6 sp :
> ff2000000004ba90
> [    1.372412]  gp : ffffffff81819c00 tp : ff60000001dc0000 t0 :
> 6900000000000000
> [    1.373527]  t1 : 0000000000000072 t2 : 6962732d76637369 s0 :
> ff2000000004bab0
> [    1.376628]  s1 : ff6000000241c410 a0 : 0000000000000008 a1 :
> ffffffff8168ca58
> [    1.379110]  a2 : 0000000000000010 a3 : 00000000000000a3 a4 :
> 0000000000000000
> [    1.380410]  a5 : 0000000000000000 a6 : 0000000000000000 a7 :
> 000000004442434e
> [    1.381019]  s2 : 0000000000000000 s3 : ff6000003fff30a0 s4 :
> ff6000000241c410
> [    1.381579]  s5 : ff600000039f9320 s6 : ff6000000241c400 s7 :
> 0000000000000002
> [    1.382242]  s8 : ffffffff81821fa0 s9 : 0000000000000000 s10:
> 0000000000000000
> [    1.384018]  s11: 0000000000000000 t3 : ffffffff81830a37 t4 :
> ffffffff81830a37
> [    1.385958]  t5 : ffffffff81830a38 t6 : ff2000000004b7c8
> [    1.387306] status: 0000000200000120 badaddr: 0000000000000008
> cause: 000000000000000d
> [    1.388407] [<ffffffff80af96e8>] mutex_lock+0x0/0x28
> [    1.389333] [<ffffffff80003dba>] msi_domain_free_irqs_all+0x2a/0x48
> [    1.390275] [<ffffffff80714e86>] platform_device_msi_free_irqs_all+0x16/0x2c
> [    1.391715] [<ffffffff808d8114>] mpxy_mbox_probe+0x6dc/0x750
> [    1.392522] [<ffffffff806f1706>] platform_probe+0x4e/0xb4
> [    1.393169] [<ffffffff806eef58>] really_probe+0x84/0x230
> [    1.393789] [<ffffffff806ef160>] __driver_probe_device+0x5c/0xdc
> [    1.394282] [<ffffffff806ef2a4>] driver_probe_device+0x2c/0xf8
> [    1.396577] [<ffffffff806ef4ac>] __driver_attach+0x6c/0x15c
> [    1.397634] [<ffffffff806ed146>] bus_for_each_dev+0x62/0xb0
> [    1.399060] [<ffffffff806eea9a>] driver_attach+0x1a/0x24
> [    1.399792] [<ffffffff806ee31e>] bus_add_driver+0xce/0x1d8
> [    1.400363] [<ffffffff806f020c>] driver_register+0x40/0xdc
> [    1.400832] [<ffffffff806f1414>] __platform_driver_register+0x1c/0x24
> [    1.401551] [<ffffffff80c3df7e>] mpxy_mbox_driver_init+0x1a/0x24
> [    1.402328] [<ffffffff800108b2>] do_one_initcall+0x56/0x1d8
> [    1.403674] [<ffffffff80c01236>] kernel_init_freeable+0x266/0x2d0
> [    1.404956] [<ffffffff80af549a>] kernel_init+0x1e/0x13c
> [    1.405422] [<ffffffff80012266>] ret_from_fork_kernel+0xe/0xcc
> [    1.405870] [<ffffffff80aff042>] ret_from_fork_kernel_asm+0x16/0x18
> 
> It is better to have the check on "mbox->msi_count" before calling
> platform_device_msi_free_irqs_all().

Right, thanks for confirming. But my point that this check should be made
inside the callee and not the caller. Can it be done once for all?

-- 
With Best Regards,
Andy Shevchenko