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    SubjectRe: crashes in prune_icache() in 2.4.26
    From
    Made a little more progress...

    Turns out the infinite loop wasn't in the CONFIG_HIGMEM while() loop, but
    rather in the while() loop at the top of the code. Sorry about that. I
    misunderstood the disassembly until now.

    So basically both types of crashes I am seeing (NULL deref and infinite
    loop) are happening in the primary/top while() loop of prune_icache()
    and I suspect they are both the result of a corrupted inode_unused list.

    Now I am trying to figure out where/how the inode_unused list is getting
    corrupted... If anyone has any existing code for validating list
    integrity, which I could sprinkle around the code, I'd love a copy.

    Thanks,
    Chris

    On Mon, 31 May 2004, Chris Caputo wrote:
    > [CC'ed lkml in case anyone else wants to take a shot.]
    >
    > A little more info... I added some printk's to the function to highlight
    > the input value of parameter 'goal' and also to show where the function
    > was returning.
    >
    > My understanding is these printk's all happened in rapid succession:
    >
    > entry > prune_icache(goal = 92370)
    > exit < prune_icache() at if (goal <= 0)
    >
    > Above the function completed without entering the CONFIG_HIGHMEM while
    > loop.
    >
    > entry > prune_icache(goal = 94037)
    > exit < prune_icache() - end of function
    >
    > Above the function went through the CONFIG_HIGHMEM while loop. This was
    > the first time this happened since boot, after a number of
    > prune_icache() calls that had returned prior to the CONFIG_HIGHMEM while
    > loop.
    >
    > entry > prune_icache(goal = 98609)
    > Unable to handle kernel NULL pointer dereference at virtual address 00000004
    >
    > The final printk above shows the function being entered and then hitting
    > the NULL dereference.
    >
    > Chris
    >
    > On Sun, 30 May 2004, Chris Caputo wrote:
    > > Hi. I have been experiencing a number of crashes in fs/inode.c's
    > > prune_icache() function. I found on linux.bkbits.net that you made the
    > > most recent major change to this function back in January. With that in
    > > mind I hope it is okay to write directly to you.
    > >
    > > I have experienced two kinds of crashes with this function.
    > >
    > > The first is in the older part of the code. Basically the inode_unused
    > > list is somehow getting corrupt and when it does an Oops happens at:
    > >
    > > entry = entry->prev; (line 808 of the 2.4.26 fs/inode.c)
    > >
    > > I haven't yet figured out how it is getting corrupt so any tips welcome.
    > >
    > > A second problem I have seen is that my system has gotten into an infinite
    > > loop in the while loop in the CONFIG_HIGHMEM part of the prune_icache()
    > > code. I haven't yet figured out why. But I am curious about the code at
    > > the beginning of the loop:
    > >
    > > while (goal-- > 0) {
    > > if (list_empty(&inode_unused_pagecache))
    > > break;
    > > entry = inode_unused_pagecache.prev;
    > > list_del(entry);
    > > list_add(entry, &inode_unused_pagecache);
    > >
    > > Is the intent of the last 3 lines to remove the entry from the end of the
    > > linked-list and then add it to the front, as a way of traversing the list?
    > > Or is it intended that the add be an add to the inode_unused list as
    > > opposed to the inode_unused_pagecache list?
    > >
    > > I'd love to figure out the problems I am experiencing, so any advice on
    > > how to proceed is welcome. The bug happens every few days on our main
    > > fileserver and I have been able to reproduce it on a test fileserver too.
    > >
    > > Chris
    >
    >
    >

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